# Factorise :/

• January 6th 2010, 11:52 AM
Mukilab
Factorise :/
$a^2-9b^2$

Don't know what to put as the subject...-1/1?
• January 6th 2010, 11:56 AM
pickslides
Quote:

Originally Posted by Mukilab
$a^2-9b^2$

$a^2-9b^2$

$a^2-3^2b^2$

$a^2-(3b)^2$

using the difference of 2 squares rule

$(a-3b)(a+3b)$

Quote:

Originally Posted by Mukilab

Don't know what to put as the subject...-1/1?

what do you mean by this?
• January 6th 2010, 12:01 PM
Mukilab
Quote:

Originally Posted by pickslides
$a^2-9b^2$

$a^2-3^2b^2$

$a^2-(3b)^2$

using the difference of 2 squares rule

$(a-3b)(a+3b)$

what do you mean by this?

I meant what should I put at the start of the quadratic, take the 'subject' as x. You would do (x ......)(x......)

Thanks for the great explanation and WIP! ^^