Hi, I need a lot of help here.

$\displaystyle F(a,b,u,u_a,u_b)=0$ with initial condition $\displaystyle u(a,0)$. Solving for $\displaystyle u_b$, find a heuristic derivation of the solution by using taylor series.

Then use that to find the solution of $\displaystyle cu_a+du_b=0$ with $\displaystyle u(a,0)=a^3$

Thank You for any help.