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(4-x)(x+5)+x2=0 la ecuación

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Solución numérica:

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Solución

Ha introducido [src]
(4 - x)*(x + 5) + x2 = 0
$$x_{2} + \left(4 - x\right) \left(x + 5\right) = 0$$
Solución detallada
Abramos la expresión en la ecuación
$$x_{2} + \left(4 - x\right) \left(x + 5\right) = 0$$
Obtenemos la ecuación cuadrática
$$- x^{2} - x + x_{2} + 20 = 0$$
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
$$a = -1$$
$$b = -1$$
$$c = x_{2} + 20$$
, entonces
D = b^2 - 4 * a * c = 

(-1)^2 - 4 * (-1) * (20 + x2) = 81 + 4*x2

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

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

o
$$x_{1} = - \frac{\sqrt{4 x_{2} + 81}}{2} - \frac{1}{2}$$
$$x_{2} = \frac{\sqrt{4 x_{2} + 81}}{2} - \frac{1}{2}$$
Gráfica
Suma y producto de raíces [src]
suma
         _______________________________                                            _______________________________                                                _______________________________                                            _______________________________                                    
      4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\     4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\         4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\     4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\
      \/  (81 + 4*re(x2))  + 16*im (x2) *cos|------------------------------|   I*\/  (81 + 4*re(x2))  + 16*im (x2) *sin|------------------------------|         \/  (81 + 4*re(x2))  + 16*im (x2) *cos|------------------------------|   I*\/  (81 + 4*re(x2))  + 16*im (x2) *sin|------------------------------|
  1                                         \              2               /                                           \              2               /     1                                         \              2               /                                           \              2               /
- - - ---------------------------------------------------------------------- - ------------------------------------------------------------------------ + - - + ---------------------------------------------------------------------- + ------------------------------------------------------------------------
  2                                     2                                                                         2                                         2                                     2                                                                         2                                    
$$\left(- \frac{i \sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} - \frac{\sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} - \frac{1}{2}\right) + \left(\frac{i \sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} + \frac{\sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} - \frac{1}{2}\right)$$
=
-1
$$-1$$
producto
/         _______________________________                                            _______________________________                                    \ /         _______________________________                                            _______________________________                                    \
|      4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\     4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\| |      4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\     4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\|
|      \/  (81 + 4*re(x2))  + 16*im (x2) *cos|------------------------------|   I*\/  (81 + 4*re(x2))  + 16*im (x2) *sin|------------------------------|| |      \/  (81 + 4*re(x2))  + 16*im (x2) *cos|------------------------------|   I*\/  (81 + 4*re(x2))  + 16*im (x2) *sin|------------------------------||
|  1                                         \              2               /                                           \              2               /| |  1                                         \              2               /                                           \              2               /|
|- - - ---------------------------------------------------------------------- - ------------------------------------------------------------------------|*|- - + ---------------------------------------------------------------------- + ------------------------------------------------------------------------|
\  2                                     2                                                                         2                                    / \  2                                     2                                                                         2                                    /
$$\left(- \frac{i \sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} - \frac{\sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} - \frac{1}{2}\right) \left(\frac{i \sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} + \frac{\sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} - \frac{1}{2}\right)$$
=
-20 - re(x2) - I*im(x2)
$$- \operatorname{re}{\left(x_{2}\right)} - i \operatorname{im}{\left(x_{2}\right)} - 20$$
-20 - re(x2) - i*im(x2)
Respuesta rápida [src]
              _______________________________                                            _______________________________                                    
           4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\     4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\
           \/  (81 + 4*re(x2))  + 16*im (x2) *cos|------------------------------|   I*\/  (81 + 4*re(x2))  + 16*im (x2) *sin|------------------------------|
       1                                         \              2               /                                           \              2               /
x1 = - - - ---------------------------------------------------------------------- - ------------------------------------------------------------------------
       2                                     2                                                                         2                                    
$$x_{1} = - \frac{i \sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} - \frac{\sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} - \frac{1}{2}$$
              _______________________________                                            _______________________________                                    
           4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\     4 /                2        2         /atan2(4*im(x2), 81 + 4*re(x2))\
           \/  (81 + 4*re(x2))  + 16*im (x2) *cos|------------------------------|   I*\/  (81 + 4*re(x2))  + 16*im (x2) *sin|------------------------------|
       1                                         \              2               /                                           \              2               /
x2 = - - + ---------------------------------------------------------------------- + ------------------------------------------------------------------------
       2                                     2                                                                         2                                    
$$x_{2} = \frac{i \sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \sin{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} + \frac{\sqrt[4]{\left(4 \operatorname{re}{\left(x_{2}\right)} + 81\right)^{2} + 16 \left(\operatorname{im}{\left(x_{2}\right)}\right)^{2}} \cos{\left(\frac{\operatorname{atan_{2}}{\left(4 \operatorname{im}{\left(x_{2}\right)},4 \operatorname{re}{\left(x_{2}\right)} + 81 \right)}}{2} \right)}}{2} - \frac{1}{2}$$
x2 = i*((4*re(x2) + 81)^2 + 16*im(x2)^2)^(1/4)*sin(atan2(4*im(x2, 4*re(x2) + 81)/2)/2 + ((4*re(x2) + 81)^2 + 16*im(x2)^2)^(1/4)*cos(atan2(4*im(x2), 4*re(x2) + 81)/2)/2 - 1/2)