Answer:
Because it is equal to (3x - 2)^2.
Step-by-step explanation:
If we factor we'll see why:
9x^2 - 12x + 4
To factor we can use the 'ac' method:
Multiplying the leading coefficient by the constant term: 9 * 4 = 36.
We need 2 numbers whose product is 36 and whose sum is -12:
These are -6 and -6 so we write:
9x^2 - 6x - 6x + 4
Factor by grouping:
= 3x(3x - 2) - 2(3x - 2)
= (3x - 2)(3x - 2)
= (3x - 2)^2 which is a perfect square.
