Dear 450081592,

1) Suppose a,b such that,

and

Then, f[g(a)]=f[g(b)]

g(a)=g(b) since f is an one to one function.

a=b since g is an one to one function.

Therefore

Hence is an one to one function.

2) Supose g(a) = c and f(c) = b,

Therefore,

Since is one to one it is invertible,

-----------A

Since f and g are one to one they are invertible.

and

Therefore -------B

From A and B,