Question

If a+b+c= 8 , a^2+b^2+c^2 = 30 then find the value of ab+bc+ca

Answer 1

Here, a+b+c=8

on squaring both sides,

(a+b+c)^2=8^2

= a^2+b^2+c^2+2(ab+bc+ca)=64

=30+2(ab+bc+ca)=64

=2(ab+bc+ca)=64-30

=2(ab+bc+ca)=34

=(ab+bc+ca)=34/2

=17

Hence, (ab+bc+ca)=17

Answer 2

the answer will be 17. you have to put the formula

${(a + b + c)}^{2}$