Question

Factor completely x^2 − 10x + 25.

Answer 1

The answer is a.
x^2 -10x+25 = x*x-2*5*x+5*5 => (x-5)(x-5)

Answer 2

We're looking for two numbers that when multiplied, give 25, and when added, give -10.

Factoring 25 leads to 5*5 or -5*-5. The second alternative also fits -5+-5 = -10.

So (x-5)(x-5) is the factorization.