Answer:
Substitution rule is one of the most important rule to solve the integrals problem.
In substitution rule we substitute different variable in such a way that it can simplify the question.
example: when we have to solve "Sin x²" we cannot solve it but
if question is "x Sin x²" we can substitute x² with t and can solve it.
The purpose of substitution rule is to simplify the problem of integrals.
