Question

If a+b+c=-5 and ab+bc+ca=15 then prove that a³+b³+c³-3abc=100
Please do and give...​

Answer 1

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

5^2 = a^2+b^2+ c^2 + 2×15

=> a^2+ b^2+ c^2= 25-30 =-5

(a+b+c)(a2+b2+c2-ab-bc-ac) = a3+b3+c3 -3abc = 100

5×(-5-15) = 5×-20= -100

proved by wt