This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
Let a_1,a_2,\ldots,a_{\phi(n)} be the positive integers less than n and relatively prime to n.

Since \gcd(a,n)=\gcd(n-a,n), the numbers  a_1,a_2,\ldots,a_{\phi(n)} are same as the numbers  n-a_1,n-a_2,\ldots,n-a_{\phi(n)} in some order. Thus,

\implies \sum\limits_{i=1}^{\phi(n)}a_i=\frac{n\phi(n)}{2}