Question
If a + b + c = 7 and ab + be + ca = 20, find the value of a2 + b2 + c2.
Solution
We know that
(a + b + c)2 = a2 + b2 + c2 + 2 (ab +bc + ca)
⇒ (7)2 = a2 + b2 + c2 + 2(20)
⇒ a2 + b2 + c2 = 9
