Question

if a + b + c = 9 and a square + b square + c square = 35 the find the value of ab + bc + ca .​ I am in need of help

Answer 1

a+b+c=9 and a2+b2+c2=35 then by using identity

(a+b+c)2=a2+b2+c2+2ab+2bc+2ca,we get the answer 9x9=35+2(ab+bc+ca)

2(ab+bc+ca)=9x9-35

2(ab+bc+ca) =81-35then we get ab+bc+ca=46/2 so ab+bc+ca=23