Question

If a+2b = 3 and ab =-5 tgen find the value of [1] a^2 + 4b^2 and [2] a^3 + 8b^3

Answer 1

1. (a+2b)^ 2 = a^2 +4b^2 + 4ab^2

(3)^2 = a^2 +4b^2 + 4(-5)^2

9 = a^2 +4b^2 + 4×25

9 = a^2 +4b^2 + 100

9-100 = a^2 + 4b^2

-91 =a^2 +4b^2