Equation is .
I have tried to substitute and I am stuck at
To be exact I do not know where to go from there in calculus sense.
Yes, that is the idea. However, just in case an overview helps...
... where (key in spoiler) ...
Spoiler:
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Don't integrate - balloontegrate!
Balloon Calculus; standard integrals, derivatives and methods
Balloon Calculus Drawing with LaTeX and Asymptote!