Question

a+b+c=12. a×a+b×b+c×c=50. find ab+bc+ca

Answer 1

(A+B+C)^2=A^2+B^2+C^2+2ab+2bc+2ca
12^2=50+2(ab+bc+ca)
144-50/2=ab+BC+ca
ab+bc+ca=47

thank you