the differintial equation given is:

(a) I did part a finding the x as a function of t when a=b

part (B) is what am having trouble with it states;

If a>b, find t as a function of x. { hint use substitution u=(sqrt(b-x))

i tried the substituon i cant seem to simpify my work after sub, is for the left side

-1/2 integral_ sqrt(b-x)du/(a-x)(u^(1/2))