HINT:
Observe that $$a(b-c)-c(b-a)=-b(c-a)$$
Put the value of $b(c-a),$ and take out common from the first two terms & the last two terms and see what happens?
HINT:
Observe that $$a(b-c)-c(b-a)=-b(c-a)$$
Put the value of $b(c-a),$ and take out common from the first two terms & the last two terms and see what happens?