Factor completely x2 - 10x + 25.

(x - 5) (x - 5)

(x + 5) (x + 5)

(x + 5) (x - 5)

(x - 25) (x - 1)

To factor a trinomial first look to the c-value (constant) and find a factor pair which adds to give the middle b-value.

25 factors

5,5

-5,-5

25, 1

-25, - 1

-5 and - 5 multiply to give 25 and add to give the middle b-value - 10

so then the solution is: (x - 5) (x - 5)