Question

If a,b,c be the p th, q th and r th terms of an AP, prove that
a(q-r)+b(r-p)+c(p-q)=0.

Please help (no shortcut )

Answer 1

a=p (given)
b=q
c=r
p(q-r) +q(r-p) +r(p-q)
pq-pr+qr-pq+pr-qr
by solving the answer is 0