Question

If a+b+C =9 and ab+bc+ca=40 find a2+b2+c2

Answer 1

(a+b+c)^2=a^2+b^2+c^2+2(ab+BC+ac)
(9)^2=a^2+b^2+c^2+2(40)
81=80+a^2+b^2+c^2
81-80=a^2+b^2+c^2

Answer 2

We Know that....

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

so by putting the values...

9^2=a^2+b^2+c^2+40

or ...

a^2+b^2+c^2=81-40
=41