Sr Examen

Ecuación diferencial dy/dx=((x+y+1)^2)-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)) = -2 + (1 + x + y(x)) 
dx                             
$$\frac{d}{d x} y{\left(x \right)} = \left(x + y{\left(x \right)} + 1\right)^{2} - 2$$
y' = (x + y + 1)^2 - 2
Solución detallada
Tenemos la ecuación:
$$- \left(x + y{\left(x \right)} + 1\right)^{2} + \frac{d}{d x} y{\left(x \right)} + 2 = 0$$
Sustituimos
$$u{\left(x \right)} = x + y{\left(x \right)} + 1$$
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
$$- x^{2} - 2 x \left(- x + u{\left(x \right)} - 1\right) - \left(- x + u{\left(x \right)} - 1\right)^{2} - 2 u{\left(x \right)} + \frac{d}{d x} \left(- x + u{\left(x \right)} - 1\right) + 3 = 0$$
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
$$\operatorname{f_{1}}{\left(x \right)} = 1$$
$$\operatorname{g_{1}}{\left(u \right)} = 1$$
$$\operatorname{f_{2}}{\left(x \right)} = -1$$
$$\operatorname{g_{2}}{\left(u \right)} = 1 - u^{2}{\left(x \right)}$$
Pasemos la ecuación a la forma:
g1(u)/g2(u)*u'= f2(x)/f1(x).

Dividamos ambos miembros de la ecuación en g2(u)
$$1 - u^{2}{\left(x \right)}$$
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
$$- \frac{\log{\left(u - 1 \right)}}{2} + \frac{\log{\left(u + 1 \right)}}{2} = Const - x$$
Solución detallada de una ecuación simple
Hemos recibido una ecuación ordinaria con la incógnica u.
(Const - es una constante)

La solución:
$$\operatorname{u_{1}} = u{\left(x \right)} = \frac{1}{\tanh{\left(C_{1} - x \right)}}$$
hacemos cambio inverso
$$y{\left(x \right)} = - x + u{\left(x \right)} - 1$$
$$y1 = y(x) = - x - 1 + \frac{1}{\tanh{\left(C_{1} - x \right)}}$$
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 *\C1  + 2*C1 + 2*(1 + C1)  + \-1 + C1  + 2*C1/*\C1  + 2*C1 + 2*(1 + C1) //   x *\3 + 3*C1 + (1 + C1)*\C1  + 2*C1 + 2*(1 + C1) / + \-1 + C1  + 2*C1/*\3 + 3*C1 + (1 + C1)*\C1  + 2*C1 + 2*(1 + C1) / + 3*(1 + C1)*\-1 + C1  + 2*C1// + 3*(1 + C1)*\-1 + C1  + 2*C1//   x *\2*C1  + 4*C1 + 7*(1 + C1)  + (1 + C1)*\3 + 3*C1 + (1 + C1)*\C1  + 2*C1 + 2*(1 + C1) / + 3*(1 + C1)*\-1 + C1  + 2*C1// + \-1 + C1  + 2*C1/*\2*C1  + 4*C1 + 7*(1 + C1) / + \-1 + C1  + 2*C1/*\2*C1  + 4*C1 + 7*(1 + C1)  + (1 + C1)*\3 + 3*C1 + (1 + C1)*\C1  + 2*C1 + 2*(1 + C1) / + 3*(1 + C1)*\-1 + C1  + 2*C1// + \-1 + C1  + 2*C1/*\2*C1  + 4*C1 + 7*(1 + C1) ///    / 6\
y(x) = C1 + x*\-1 + C1  + 2*C1/ + x *\1 + C1 + (1 + C1)*\-1 + C1  + 2*C1// + ---------------------------------------------------------------------------- + -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- + ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ + O\x /
                                                                                                                  3                                                                                                                                   6                                                                                                                                                                                                                                                                                 15                                                                                                                                                                                           
$$y{\left(x \right)} = x \left(C_{1}^{2} + 2 C_{1} - 1\right) + x^{2} \left(C_{1} + \left(C_{1} + 1\right) \left(C_{1}^{2} + 2 C_{1} - 1\right) + 1\right) + \frac{x^{3} \left(C_{1}^{2} + 2 C_{1} + 2 \left(C_{1} + 1\right)^{2} + \left(C_{1}^{2} + 2 C_{1} - 1\right) \left(C_{1}^{2} + 2 C_{1} + 2 \left(C_{1} + 1\right)^{2}\right)\right)}{3} + \frac{x^{4} \left(3 C_{1} + 3 \left(C_{1} + 1\right) \left(C_{1}^{2} + 2 C_{1} - 1\right) + \left(C_{1} + 1\right) \left(C_{1}^{2} + 2 C_{1} + 2 \left(C_{1} + 1\right)^{2}\right) + \left(C_{1}^{2} + 2 C_{1} - 1\right) \left(3 C_{1} + 3 \left(C_{1} + 1\right) \left(C_{1}^{2} + 2 C_{1} - 1\right) + \left(C_{1} + 1\right) \left(C_{1}^{2} + 2 C_{1} + 2 \left(C_{1} + 1\right)^{2}\right) + 3\right) + 3\right)}{6} + \frac{x^{5} \left(2 C_{1}^{2} + 4 C_{1} + 7 \left(C_{1} + 1\right)^{2} + \left(C_{1} + 1\right) \left(3 C_{1} + 3 \left(C_{1} + 1\right) \left(C_{1}^{2} + 2 C_{1} - 1\right) + \left(C_{1} + 1\right) \left(C_{1}^{2} + 2 C_{1} + 2 \left(C_{1} + 1\right)^{2}\right) + 3\right) + \left(C_{1}^{2} + 2 C_{1} - 1\right) \left(2 C_{1}^{2} + 4 C_{1} + 7 \left(C_{1} + 1\right)^{2}\right) + \left(C_{1}^{2} + 2 C_{1} - 1\right) \left(2 C_{1}^{2} + 4 C_{1} + 7 \left(C_{1} + 1\right)^{2} + \left(C_{1} + 1\right) \left(3 C_{1} + 3 \left(C_{1} + 1\right) \left(C_{1}^{2} + 2 C_{1} - 1\right) + \left(C_{1} + 1\right) \left(C_{1}^{2} + 2 C_{1} + 2 \left(C_{1} + 1\right)^{2}\right) + 3\right) + \left(C_{1}^{2} + 2 C_{1} - 1\right) \left(2 C_{1}^{2} + 4 C_{1} + 7 \left(C_{1} + 1\right)^{2}\right)\right)\right)}{15} + C_{1} + O\left(x^{6}\right)$$
Gráfico para el problema de Cauchy
Clasificación
1st power series
lie group
Respuesta numérica [src]
(x, y):
(-10.0, 0.75)
(-7.777777777777778, 5.759197819048073)
(-5.555555555555555, 3.5553393419934953)
(-3.333333333333333, 1.3333307975451014)
(-1.1111111111111107, -0.8888889180717234)
(1.1111111111111107, -3.111111109868568)
(3.333333333333334, -5.333333332612546)
(5.555555555555557, -7.555555555366128)
(7.777777777777779, -9.77777777761853)
(10.0, -11.999999999870932)
(10.0, -11.999999999870932)