Question

What is the complete factorization of the trinomial x^2-8x+16?

A.
(x – 4)(x – 4)
B.
(x – 2)(x + 8)
C.
(x – 1)(x – 16)
D.
(x + 4)(x – 4)

Answer 1

A. (x-4)(x-4)

Explanation:

Note that (x+a)(x+b)=x²+(a+b)x+ab.

Looking at this with regard to our trinomial, x²-8x+16, in our case we could say that a+b=-8 and ab=16.

Since ab=16, we know a and b are pairs of factors of 16. So a and b are either (1 and 16), (2 and 8), (4 and 4).

We also know that a+b=-8, so which pair of factors above can be added or subtracted from each other to get -8? 4 and 4, or rather, -4 and -4.

So, since (x+a)(x+b)=x²+(a+b)x+ab, and in our case 'a' and 'b' are both -4, we can say that x²-8x+16=(x-4)(x-4).