Question

14. If a+b+c=6 and a +b + c =20, find ab+bc+ca?​

Answer 1

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

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

6^2= 20+2(ab+bc+ca) ( Substituting the given values)

36= 20+2(ab+bc+ ca)

36 - 20 = 2(ab+bc+ca) (solving)

16 = 2(ab+bc+ ca)

8 = ab+bc+ca

Hope this helps!