Hey! :o
I have to find the solution of the problem $$u_t(x,t)+u_x(x,t)=\frac{2x}{1+(x-t)^2}u^2(x,t), x \in \mathbb{R}, t>0 \\ u(x,0)=1, x \in \mathbb{R}$$
I found that the solution is $$u(x, t)=\frac{1+x^2-2xt+t^2}{x^2-4xt+2t^2+1}$$
Now we have to look for which values this solution is...