Question

using algebraic identities. if a + b + c = 9 and AB + BC + CA = 40, then find value of a2+ b2+ c2.​

Answer 1

(a+b+c)2=a2+b2+c2+2(ab+bc+ca)

(9)2=a2+b2+c2+2(40)

81=a2+b2+c2+80

81-80=a2+b2+c2

1=a2+b2+c2