Question

Simplify $3a^2(5a^2-3a-24)$ and also find its value for

(i) a = 1 (ii) a = 2.

(4 marks)

Answer 1

$3a^2(5a^2-3a-24)=15a^4-9a^3-72a^2$

$\left(i\right)a=1$

$\Rightarrow 15(1{)}^4-9(1{)}^3-72(1{)}^2$

$=15\left(1\right)-9\left(1\right)-72\left(1\right)$

$=-66$

(2 marks)

$\left(ii\right)a=2$

$\Rightarrow 15(2{)}^4-9(2{)}^3-72(2{)}^2$

$=15\left(16\right)-9\left(8\right)-72\left(4\right)$

$=240-72-288$

$=-120$
(2 marks)