Question

if a^2+b^2+c^2=80 and a+b+c=20,then find the value of ab+bc+ca​

Answer 1

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

(20)^2=80+2(ab+BC+ca)

400-80= 2(ab+BC+ca)

ab + BC +ca = 320/2

160