Question

Simplify $3x\left(4x-5\right)+3$ and find its value for (i)$x=3$
(ii) $x=\frac{1}{2}$

Answer 1

$3x(4x-5)+3=12x^2-15x+13$

(i)For $x=3$

$=12(3{)}^2-15(3)+13$

$=108+3-45$

$=66$

(ii)$x=\frac{1}{2}$

$12x^2-15x+3=12{\left(\frac{1}{2}\right)}^2-15\left(\frac{1}{2}\right)+3$

$=3-\frac{15}{2}+3=6-\frac{15}{2}=\frac{-3}{2}$.