x2-1=(x-1)(x+1)
It factors out like this because it's the difference of two squares. It only works with subtraction and is always in the format with two groups of parenthases. For example: 16x-4. 16 and 4 are both squares, so it factors out like this: (4x+2)(4x-2). One set is always minus, the other is always plus. The order doesn't matter.
What about it? Factorise it?
x(x - 7)
13X squared + 7X + 12
X2 - 4= (x + 2)(x - 2)===========
5x2 + 9x + 13 has no real factors.
( x2 - 121 ) = (x + 11) times (x - 11)
3x2 - 8x = x(3x - 8)
(x - 3)(2x - 7)
(x + 2)(x + 1)
Factorise it: (x + 5)(3x - 8)
X squared + 7X + 12?
It is (x+5)(x+1) when factored