Composition of the functions is
commutative.

See below.

Step-by-step explanation:

Composition of the functions is sometimes commutative.

Under certain circumstances, they can be the same. However, most of the time, they are not commutative.

For instance, if we have f(x)=x^2 and g(x)=x^3, then:

Most of the time, however, this won't work.

Edit: Added an example.

not only in mathematics, scientific proof also are required in the other field of science. also maths proofs are of particular structure, containing steps and logics. so proving is like doing science, it is science. that's why it is important to prove. 

an inaccurate proof leads to errors, or stating results that are not accurate.  which wil mess the probelm up you dont want this