Question

If a+b+c=8, ab+bc+ac=20, find the value of a square+b square+c square

Answer 1

a+b+c=8. Square it on both sides. a^2+b^2+c^2+2ab+2bc+2ca=512. =>a^2+b^2+c^2+2(ab+bc+ca)=512. =>a^2+b^2+c^2+40=512. =>a^2+b^2+c^2=472.