Algebra
posted by Katie .
x^33x^2+3x9=0. My book factors it to x^2(x3)+3(x3)=0, but then it magically becomes (x3)(x^2+3). I have no idea how it became these numbers. Could you explain please? Thanks!

you have a common factor, x3. Let me use w for it.
x^2*w+3w=
w(x^2+3)
(x3)(x^2+3)