Initial value problem $y”=e^{2y}, y(0)=0, y'(0)=1$

initial-value-problemsordinary differential equations

Supposedly, it is possible to determine information about the constants of this IVP solution, without computing the solution of the differential equation. Here's how I solve this.

Let $z=y'$. In brief, we then have the separable equation $$z\frac{dz}{dy}=f(y,z)=e^{2y}$$

and solving for $z$ $$z=\sqrt{e^{2y}+c}$$

which can be made into a separable equation and integrated. After playing around with the initial conditions, I did find that $c=0$. But this is a contradiction with the results of the second separable equation. Can we really solve $c$ before finding the explicit form of $y$?

Best Answer

From my answer to this, we see that we need to take the $+$ of the square root and the answer will be case $3$ where $C_1=0$. Thus the answer is

$$y=-\log(1-x)$$

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