text: ok i can't do this for some reason.  how do u factor this 4x^2-36x+81???   this is pretty simple   4x^2 = (2x)^2 81 = 9^2 is -36x = -2(2x)9 yes  so we get((2x)^2-2(2x)9+9^2) = (2x-9)^2  another way try to sqaure it by putrting 81 = a + b so that   4x^2-36x+a is a perfect square (2x)^2-2(2x)9 + +9^2 is a perfect square  so a =81 and b =0  we get(2x-9)^2  1st method works when we know the pattern and second method for all cases. whole square falls into it