Q: How should I solve the following exercise:
Give the particular solution to the following boundary value problem:
$$\frac{dy}{dx} = ({\ln{e^x}})^{1/y}, \, \hspace{3mm} y(1) = -1$$
I know that $\ln(e^x) = x$ so that the problem comes down to solving
$$y = x^{1/y}dx, \hspace{5mm} y(1) = -1$$
But I can't get much further..
$$dy/dx = ln(e^x)^{1/y}, y(1) = -1$$ $$dy/dx = ln(e^x)^{1/y}$$
$$(e^x)^{1/y}=e^{x/y}$$ $$dy/dx = ln(e^{x/y})=\frac{x}{y}$$ $$\frac{dy}{dx}=\frac{x}{y}$$ $$\frac{ y^2}{ 2}=\frac{x^2}{2}+C$$
Given $y(1)=-1$
$$\frac{ (-1)^2}{ 2}=\frac{1^2}{2}+C$$ $$C=0$$
$$\frac{ y^2}{ 2}=\frac{x^2}{2}$$ $$y^2-x^2=0$$