Sr Examen

Ecuación diferencial dy/dx=(x+y-7)^2

El profesor se sorprenderá mucho al ver tu solución correcta😉

v

Para el problema de Cauchy:

y() =
y'() =
y''() =
y'''() =
y''''() =

Gráfico:

interior superior

Solución

Ha introducido [src]
d                         2
--(y(x)) = (-7 + x + y(x)) 
dx                         
$$\frac{d}{d x} y{\left(x \right)} = \left(x + y{\left(x \right)} - 7\right)^{2}$$
y' = (x + y - 7)^2
Solución detallada
Tenemos la ecuación:
$$- \left(x + y{\left(x \right)} - 7\right)^{2} + \frac{d}{d x} y{\left(x \right)} = 0$$
Sustituimos
$$u{\left(x \right)} = x + y{\left(x \right)} - 7$$
y porque
$$\frac{d}{d x} y{\left(x \right)} + 1 = \frac{d}{d x} u{\left(x \right)}$$
entonces
$$\frac{d}{d x} y{\left(x \right)} = \frac{d}{d x} u{\left(x \right)} - 1$$
sustituimos
$$- x^{2} - 2 x \left(- x + u{\left(x \right)} + 7\right) - \left(- x + u{\left(x \right)} + 7\right)^{2} + 14 u{\left(x \right)} + \frac{d}{d x} \left(- x + u{\left(x \right)} + 7\right) + 49 = 0$$
o
$$- u^{2}{\left(x \right)} + \frac{d}{d x} u{\left(x \right)} - 1 = 0$$
Esta ecuación diferencial tiene la forma:
f1(x)*g1(u)*u' = f2(x)*g2(u),

donde
$$\operatorname{f_{1}}{\left(x \right)} = 1$$
$$\operatorname{g_{1}}{\left(u \right)} = 1$$
$$\operatorname{f_{2}}{\left(x \right)} = -1$$
$$\operatorname{g_{2}}{\left(u \right)} = - u^{2}{\left(x \right)} - 1$$
Pasemos la ecuación a la forma:
g1(u)/g2(u)*u'= f2(x)/f1(x).

Dividamos ambos miembros de la ecuación en g2(u)
$$- u^{2}{\left(x \right)} - 1$$
obtendremos
$$- \frac{\frac{d}{d x} u{\left(x \right)}}{u^{2}{\left(x \right)} + 1} = -1$$
Con esto hemos separado las variables x y u.

Ahora multipliquemos las dos partes de la ecuación por dx,
entonces la ecuación será así
$$- \frac{dx \frac{d}{d x} u{\left(x \right)}}{u^{2}{\left(x \right)} + 1} = - dx$$
o
$$- \frac{du}{u^{2}{\left(x \right)} + 1} = - dx$$

Tomemos la integral de las dos partes de la ecuación:
- de la parte izquierda la integral por u,
- de la parte derecha la integral por x.
$$\int \left(- \frac{1}{u^{2} + 1}\right)\, du = \int \left(-1\right)\, dx$$
Solución detallada de la integral con u
Solución detallada de la integral con x
Tomemos estas integrales
$$- \operatorname{atan}{\left(u \right)} = Const - x$$
Solución detallada de una ecuación simple
Hemos recibido una ecuación ordinaria con la incógnica u.
(Const - es una constante)

La solución:
$$\operatorname{u_{1}} = u{\left(x \right)} = - \tan{\left(C_{1} - x \right)}$$
hacemos cambio inverso
$$y{\left(x \right)} = - x + u{\left(x \right)} + 7$$
$$y1 = y(x) = - x - \tan{\left(C_{1} - x \right)} + 7$$
Respuesta [src]
                                                                                  3 /       2                      2   /       2        \ /       2                      2\\    4 /                       /       2                      2\   /       2        \ /                       /       2                      2\               /       2        \\               /       2        \\    5 /                  2              2             /                       /       2                      2\               /       2        \\   /       2        \ /                  2              2\   /       2        \ /                  2              2             /                       /       2                      2\               /       2        \\   /       2        \ /                  2              2\\\        
              /       2        \    2 /                    /       2        \\   x *\50 + C1  - 14*C1 + 2*(-7 + C1)  + \49 + C1  - 14*C1/*\50 + C1  - 14*C1 + 2*(-7 + C1) //   x *\-21 + 3*C1 + (-7 + C1)*\50 + C1  - 14*C1 + 2*(-7 + C1) / + \49 + C1  - 14*C1/*\-21 + 3*C1 + (-7 + C1)*\50 + C1  - 14*C1 + 2*(-7 + C1) / + 3*(-7 + C1)*\49 + C1  - 14*C1// + 3*(-7 + C1)*\49 + C1  - 14*C1//   x *\100 - 28*C1 + 2*C1  + 7*(-7 + C1)  + (-7 + C1)*\-21 + 3*C1 + (-7 + C1)*\50 + C1  - 14*C1 + 2*(-7 + C1) / + 3*(-7 + C1)*\49 + C1  - 14*C1// + \49 + C1  - 14*C1/*\100 - 28*C1 + 2*C1  + 7*(-7 + C1) / + \49 + C1  - 14*C1/*\100 - 28*C1 + 2*C1  + 7*(-7 + C1)  + (-7 + C1)*\-21 + 3*C1 + (-7 + C1)*\50 + C1  - 14*C1 + 2*(-7 + C1) / + 3*(-7 + C1)*\49 + C1  - 14*C1// + \49 + C1  - 14*C1/*\100 - 28*C1 + 2*C1  + 7*(-7 + C1) ///    / 6\
y(x) = C1 + x*\49 + C1  - 14*C1/ + x *\-7 + C1 + (-7 + C1)*\49 + C1  - 14*C1// + ------------------------------------------------------------------------------------------- + --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- + ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- + O\x /
                                                                                                                              3                                                                                                                                                       6                                                                                                                                                                                                                                                                                                                            15                                                                                                                                                                                                                         
$$y{\left(x \right)} = x \left(C_{1}^{2} - 14 C_{1} + 49\right) + x^{2} \left(C_{1} + \left(C_{1} - 7\right) \left(C_{1}^{2} - 14 C_{1} + 49\right) - 7\right) + \frac{x^{3} \left(C_{1}^{2} - 14 C_{1} + 2 \left(C_{1} - 7\right)^{2} + \left(C_{1}^{2} - 14 C_{1} + 49\right) \left(C_{1}^{2} - 14 C_{1} + 2 \left(C_{1} - 7\right)^{2} + 50\right) + 50\right)}{3} + \frac{x^{4} \left(3 C_{1} + 3 \left(C_{1} - 7\right) \left(C_{1}^{2} - 14 C_{1} + 49\right) + \left(C_{1} - 7\right) \left(C_{1}^{2} - 14 C_{1} + 2 \left(C_{1} - 7\right)^{2} + 50\right) + \left(C_{1}^{2} - 14 C_{1} + 49\right) \left(3 C_{1} + 3 \left(C_{1} - 7\right) \left(C_{1}^{2} - 14 C_{1} + 49\right) + \left(C_{1} - 7\right) \left(C_{1}^{2} - 14 C_{1} + 2 \left(C_{1} - 7\right)^{2} + 50\right) - 21\right) - 21\right)}{6} + \frac{x^{5} \left(2 C_{1}^{2} - 28 C_{1} + 7 \left(C_{1} - 7\right)^{2} + \left(C_{1} - 7\right) \left(3 C_{1} + 3 \left(C_{1} - 7\right) \left(C_{1}^{2} - 14 C_{1} + 49\right) + \left(C_{1} - 7\right) \left(C_{1}^{2} - 14 C_{1} + 2 \left(C_{1} - 7\right)^{2} + 50\right) - 21\right) + \left(C_{1}^{2} - 14 C_{1} + 49\right) \left(2 C_{1}^{2} - 28 C_{1} + 7 \left(C_{1} - 7\right)^{2} + 100\right) + \left(C_{1}^{2} - 14 C_{1} + 49\right) \left(2 C_{1}^{2} - 28 C_{1} + 7 \left(C_{1} - 7\right)^{2} + \left(C_{1} - 7\right) \left(3 C_{1} + 3 \left(C_{1} - 7\right) \left(C_{1}^{2} - 14 C_{1} + 49\right) + \left(C_{1} - 7\right) \left(C_{1}^{2} - 14 C_{1} + 2 \left(C_{1} - 7\right)^{2} + 50\right) - 21\right) + \left(C_{1}^{2} - 14 C_{1} + 49\right) \left(2 C_{1}^{2} - 28 C_{1} + 7 \left(C_{1} - 7\right)^{2} + 100\right) + 100\right) + 100\right)}{15} + C_{1} + O\left(x^{6}\right)$$
Gráfico para el problema de Cauchy
Clasificación
1st power series
lie group
Respuesta numérica [src]
(x, y):
(-10.0, 0.75)
(-7.777777777777778, 15.642339349557037)
(-5.555555555555555, 494494074302.16876)
(-3.333333333333333, nan)
(-1.1111111111111107, 2.78363573e-315)
(1.1111111111111107, 8.427456047434801e+197)
(3.333333333333334, 3.1933833808213433e-248)
(5.555555555555557, 2.125757255287192e+160)
(7.777777777777779, 8.388243567338116e+296)
(10.0, 3.861029683e-315)
(10.0, 3.861029683e-315)