Question

I want to know how to vertify that a function is inverse step by step

Answer 1

call one function
\[f\] the other
\[g\] and then check that the composite function
\[f(g(x))=x\]and
\[g(f(x))=x\]

Answer 2

in other words when you compose them you get the identity function back
identity function:
\[I(x)=x\]