Question

Simplify $3x(4x-5)+3$ and find its values for $x=3$

Answer 1

$3x(4x-5)+3$

$=12x^2-15x+3$

$=3(4x^2-5x+1)$

$=3(4x^2-4x-x+1)$

$=3(4x(x-1)-1(x-1))$

$=3(4x-1)(x-1)$ at $x=3$

$=3(4\times 3-1)(3-1)$

$=3(12-1)\times 2$

$=3\times 11\times 2=66$