Definition of  Inverse Functions:

 

If f(x)=x+1\displaystyle {f{{\left({x}\right)}}}={x}+{1} and g(x)=x1\displaystyle {g{{\left({x}\right)}}}={x}-{1},
(a) f(g(x))=\displaystyle {f{{\left({g{{\left({x}\right)}}}\right)}}}=  
(b) g(f(x))=\displaystyle {g{{\left({f{{\left({x}\right)}}}\right)}}}=  
(c) Thus g(x)\displaystyle {g{{\left({x}\right)}}} is called an function of f(x)\displaystyle {f{{\left({x}\right)}}}