Question

if a²+b²+c² = 90 and a+ b+ c = 20 , then find the value of ab + bc +ca.

Answer 1

Answer:

155

Step-by-step explanation:

Given a2+b2+c2=90

and also a+b+c=20

Squaring on both sides

(a+b+c)2=400

(a2+b2+c2)+2(ab+bc+ca)=400

⟹2(ab+bc+ca)=400−90=310⟹ab+bc+ca=155