Question

if a+b+c=9 and ab+bc+ca=26 find 3a+5y=15?​

Answer 1

Answer:

Given a+b+c=9 & ab+bc+ca=26

As a3+b3+c3−3abc=(a+b+c)(a2+b2+c2−ab−bc−ca)

⇒(a3+b3+c3−abc)=(a+b+c)[(a+b+c)2−3(ab+bc+ca)]

⇒(a3+b3+c3−3abc)=9[81−78]=27