# Factorise

• November 26th 2008, 05:10 PM
Joker37
Factorise
-3(5x - 8)^2 + 27
• November 26th 2008, 05:29 PM
Linnus
$-3(5x - 8)^2 + 27$
Foil it first
$-3[25x^2-80x+64]+27$
Distribute the -3
$-75x^2+240x-192+27$
$-75x^2+240x-165$
Factor out a -15
$-15[5x^2-16x+11]$
factor
$-15(x-1)(5x-11)$
• November 26th 2008, 11:07 PM
Prove It
Quote:

Originally Posted by Joker37
-3(5x - 8)^2 + 27

Easier to take out -3 as a common factor and then DOTS.

$-3(5x - 8)^2 + 27 = -3[(5x - 8)^2 - 9]$

$= -3[(5x - 8)^2 - 3^2]$

$= -3[(5x - 8 + 3)(5x - 8 - 3)]$

$= -3(5x - 5)(5x - 11)$

$= -15(x-1)(5x-11)$.