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z=x^2+2*y^2-2*x*y-10*x+10*y+20 la ecuación

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Solución numérica:

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Solución

Ha introducido [src]
     2      2                           
z = x  + 2*y  - 2*x*y - 10*x + 10*y + 20
$$z = \left(10 y + \left(- 10 x + \left(- 2 x y + \left(x^{2} + 2 y^{2}\right)\right)\right)\right) + 20$$
Solución detallada
Transportemos el miembro derecho de la ecuación al
miembro izquierdo de la ecuación con el signo negativo.

La ecuación se convierte de
$$z = \left(10 y + \left(- 10 x + \left(- 2 x y + \left(x^{2} + 2 y^{2}\right)\right)\right)\right) + 20$$
en
$$z + \left(\left(- 10 y + \left(10 x + \left(2 x y + \left(- x^{2} - 2 y^{2}\right)\right)\right)\right) - 20\right) = 0$$
Es la ecuación de la forma
a*x^2 + b*x + c = 0

La ecuación cuadrática puede ser resuelta
con la ayuda del discriminante.
Las raíces de la ecuación cuadrática:
$$x_{1} = \frac{\sqrt{D} - b}{2 a}$$
$$x_{2} = \frac{- \sqrt{D} - b}{2 a}$$
donde D = b^2 - 4*a*c es el discriminante.
Como
$$a = -1$$
$$b = 2 y + 10$$
$$c = - 2 y^{2} - 10 y + z - 20$$
, entonces
D = b^2 - 4 * a * c = 

(10 + 2*y)^2 - 4 * (-1) * (-20 + z - 10*y - 2*y^2) = -80 + (10 + 2*y)^2 - 40*y - 8*y^2 + 4*z

La ecuación tiene dos raíces.
x1 = (-b + sqrt(D)) / (2*a)

x2 = (-b - sqrt(D)) / (2*a)

o
$$x_{1} = y - \frac{\sqrt{- 8 y^{2} - 40 y + 4 z + \left(2 y + 10\right)^{2} - 80}}{2} + 5$$
$$x_{2} = y + \frac{\sqrt{- 8 y^{2} - 40 y + 4 z + \left(2 y + 10\right)^{2} - 80}}{2} + 5$$
Teorema de Cardano-Vieta
reescribamos la ecuación
$$z = \left(10 y + \left(- 10 x + \left(- 2 x y + \left(x^{2} + 2 y^{2}\right)\right)\right)\right) + 20$$
de
$$a x^{2} + b x + c = 0$$
como ecuación cuadrática reducida
$$x^{2} + \frac{b x}{a} + \frac{c}{a} = 0$$
$$x^{2} - 2 x y - 10 x + 2 y^{2} + 10 y - z + 20 = 0$$
$$p x + q + x^{2} = 0$$
donde
$$p = \frac{b}{a}$$
$$p = - 2 y - 10$$
$$q = \frac{c}{a}$$
$$q = 2 y^{2} + 10 y - z + 20$$
Fórmulas de Cardano-Vieta
$$x_{1} + x_{2} = - p$$
$$x_{1} x_{2} = q$$
$$x_{1} + x_{2} = 2 y + 10$$
$$x_{1} x_{2} = 2 y^{2} + 10 y - z + 20$$
Gráfica
Respuesta rápida [src]
           /      ____________________________________________________________                                                                        \       ____________________________________________________________                                                                        
           |     /                                                          2     /     /                              2        2           \\        |      /                                                          2     /     /                              2        2           \\        
           |  4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        |   4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        
x1 = 5 + I*|- \/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *sin|----------------------------------------------------------| + im(y)| - \/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *cos|----------------------------------------------------------| + re(y)
           \                                                                      \                            2                             /        /                                                                       \                            2                             /        
$$x_{1} = i \left(- \sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{im}{\left(y\right)}\right) - \sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{re}{\left(y\right)} + 5$$
           /    ____________________________________________________________                                                                        \       ____________________________________________________________                                                                        
           |   /                                                          2     /     /                              2        2           \\        |      /                                                          2     /     /                              2        2           \\        
           |4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        |   4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        
x2 = 5 + I*|\/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *sin|----------------------------------------------------------| + im(y)| + \/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *cos|----------------------------------------------------------| + re(y)
           \                                                                    \                            2                             /        /                                                                       \                            2                             /        
$$x_{2} = i \left(\sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{im}{\left(y\right)}\right) + \sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{re}{\left(y\right)} + 5$$
x2 = i*(((-2*re(y)*im(y) + im(z))^2 + (-re(y)^2 + re(z) + im(y)^2 + 5)^2)^(1/4)*sin(atan2(-2*re(y)*im(y) + im(z, -re(y)^2 + re(z) + im(y)^2 + 5)/2) + im(y)) + ((-2*re(y)*im(y) + im(z))^2 + (-re(y)^2 + re(z) + im(y)^2 + 5)^2)^(1/4)*cos(atan2(-2*re(y)*im(y) + im(z), -re(y)^2 + re(z) + im(y)^2 + 5)/2) + re(y) + 5)
Suma y producto de raíces [src]
suma
      /      ____________________________________________________________                                                                        \       ____________________________________________________________                                                                                 /    ____________________________________________________________                                                                        \       ____________________________________________________________                                                                        
      |     /                                                          2     /     /                              2        2           \\        |      /                                                          2     /     /                              2        2           \\                 |   /                                                          2     /     /                              2        2           \\        |      /                                                          2     /     /                              2        2           \\        
      |  4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        |   4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|                 |4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        |   4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        
5 + I*|- \/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *sin|----------------------------------------------------------| + im(y)| - \/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *cos|----------------------------------------------------------| + re(y) + 5 + I*|\/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *sin|----------------------------------------------------------| + im(y)| + \/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *cos|----------------------------------------------------------| + re(y)
      \                                                                      \                            2                             /        /                                                                       \                            2                             /                 \                                                                    \                            2                             /        /                                                                       \                            2                             /        
$$\left(i \left(- \sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{im}{\left(y\right)}\right) - \sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{re}{\left(y\right)} + 5\right) + \left(i \left(\sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{im}{\left(y\right)}\right) + \sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{re}{\left(y\right)} + 5\right)$$
=
                 /    ____________________________________________________________                                                                        \     /      ____________________________________________________________                                                                        \
                 |   /                                                          2     /     /                              2        2           \\        |     |     /                                                          2     /     /                              2        2           \\        |
                 |4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        |     |  4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        |
10 + 2*re(y) + I*|\/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *sin|----------------------------------------------------------| + im(y)| + I*|- \/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *sin|----------------------------------------------------------| + im(y)|
                 \                                                                    \                            2                             /        /     \                                                                      \                            2                             /        /
$$i \left(- \sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{im}{\left(y\right)}\right) + i \left(\sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{im}{\left(y\right)}\right) + 2 \operatorname{re}{\left(y\right)} + 10$$
producto
/      /      ____________________________________________________________                                                                        \       ____________________________________________________________                                                                        \ /      /    ____________________________________________________________                                                                        \       ____________________________________________________________                                                                        \
|      |     /                                                          2     /     /                              2        2           \\        |      /                                                          2     /     /                              2        2           \\        | |      |   /                                                          2     /     /                              2        2           \\        |      /                                                          2     /     /                              2        2           \\        |
|      |  4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        |   4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        | |      |4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        |   4 /                          2   /      2        2           \      |atan2\-2*im(y)*re(y) + im(z), 5 + im (y) - re (y) + re(z)/|        |
|5 + I*|- \/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *sin|----------------------------------------------------------| + im(y)| - \/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *cos|----------------------------------------------------------| + re(y)|*|5 + I*|\/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *sin|----------------------------------------------------------| + im(y)| + \/   (-2*im(y)*re(y) + im(z))  + \5 + im (y) - re (y) + re(z)/  *cos|----------------------------------------------------------| + re(y)|
\      \                                                                      \                            2                             /        /                                                                       \                            2                             /        / \      \                                                                    \                            2                             /        /                                                                       \                            2                             /        /
$$\left(i \left(- \sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{im}{\left(y\right)}\right) - \sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{re}{\left(y\right)} + 5\right) \left(i \left(\sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{im}{\left(y\right)}\right) + \sqrt[4]{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)}\right)^{2} + \left(- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(- 2 \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + \operatorname{im}{\left(z\right)},- \left(\operatorname{re}{\left(y\right)}\right)^{2} + \operatorname{re}{\left(z\right)} + \left(\operatorname{im}{\left(y\right)}\right)^{2} + 5 \right)}}{2} \right)} + \operatorname{re}{\left(y\right)} + 5\right)$$
=
                 2          2                                                       
20 - re(z) - 2*im (y) + 2*re (y) + 10*re(y) - I*im(z) + 10*I*im(y) + 4*I*im(y)*re(y)
$$2 \left(\operatorname{re}{\left(y\right)}\right)^{2} + 4 i \operatorname{re}{\left(y\right)} \operatorname{im}{\left(y\right)} + 10 \operatorname{re}{\left(y\right)} - \operatorname{re}{\left(z\right)} - 2 \left(\operatorname{im}{\left(y\right)}\right)^{2} + 10 i \operatorname{im}{\left(y\right)} - i \operatorname{im}{\left(z\right)} + 20$$
20 - re(z) - 2*im(y)^2 + 2*re(y)^2 + 10*re(y) - i*im(z) + 10*i*im(y) + 4*i*im(y)*re(y)