X squared + 7X + 12?
It is: x(x-3) factorized
x(x - 7)
x(x-7)
7x-x2 = x(7-x)
What about it? Factorise it?
x2 + 4x = x(x + 4)
13X squared + 7X + 12
X2 - 4= (x + 2)(x - 2)===========
(x + 2)(x + 1)
x2 - 41 cannot be factorised.
( x2 - 121 ) = (x + 11) times (x - 11)