hi,

I advanced in my problem but I'm again in trouble

I transformed my expression with polar coordinates

so (c is my constant)

Now I have to find the value of my constant by caracteristics method

so I continue my reasoning:

such as

such as

we find before that

moreover with my initial condition

so i guess

for t=0,

donc que

so

in short I feel that's wrong

someone can help me please??

thanks