how do i factor 4xx-36?

4xx - 36 can also be written as

4x^2 - 36
to factor this, notice that 4x^2 and 36 are both perfect squares (meaning they have an exact squareroot),, and 4x^2 - 36 is a difference of two squares.
recall that if an expression is in the form (a^2 - b^2) it can also be written as
(a+b)(a-b)
where a and b are the squareroots of a^2 and b^2 respectively
now we get their squareroots:
sqrt(4x^2) = 2x
sqrt(36) = 6
thus
(2x+6)(2x-6)

hope this helps~ :)