Question

A+b+c=9 ab+bc+ca=10 find a2 +b2+c2

Answer 1

(a+b+c)²=a2+b2+c2 + 2(ab+bc+ca)

(9)²= a2+b2+c2 + 2(10)

18 = a2+b2+c2 + 20

a2+b2+c2 = 20-18

a2+b2+c2 = 2

Answer 2

we know that

( a+b+c)^2 = (a^2 + b^2 + c^2) + 2( ab +bc + ca)

(9)^2 = a^2 + b^2 + c^2 + 2 (10)

81 = a^2 + b^2 + c^2 + 20

a^2 + b^2 + c^2 = 81 - 20

= 61