# Prove that if \$n>1\$, the sum of positive integers less than \$n\$ and coprime to \$n\$ is \$(1/2)na(n)\$ where…

Question 12(iii) Could anyone explain this part of the question to me.

What i tried
co-prime means that the two integers a and b are said to be relatively prime, mutually prime, or coprime (also written co-prime) if the only positive integer (factor) that divides both of them is 1

Take th number $$3$$ for example, then the sum of integers less than $$3$$ and co-prime to $$3$$ is $$2+1=3$$, $$2$$ and $$1$$ are the two integers co-prime to $$3$$ which thus satisfies the formula $$0.5*n*a(n)$$ where $$n=3$$, $$a(n)=2$$. However im unsure of how to prove it. Could anyone explain. Thanks