Evaluate expression (b - a)(a + b) a b - 3 a b^3 + 3a^3 b

[yohanson77]

I'm lost on this, and keep getting wrong answer:-(

Q. Evaluate the expression

(b - a)(a + b) a b - 3 a b^3 + 3a^3 b

when b = 2

Can someone please help?

yours

yohanson77

 

[skeeter]

as you wrote it ...

(b-a) (a+b) ab - 3ab(cubed) + 3a(cubed)b

b = 2 ...

(2-a)(a+2)(a*2) - 3a(2)³ + 3a³(2) =

(4 - a²)(2a) - 24a + 6a³ =

8a - 2a³ - 24a + 6a³ =

4a³ - 16a