I use the railroad method so here's how I would solve it:
4 x 25 = 100
10 x 10 = 100, 10 + 10 = 20
(x +10/4)(x + 10/4)
(x + 5/2)(x + 5/2)
The answer should be: (2x + 5)(2x + 5)
It can be checked:
2x x 2x = 4x^2
2x x 5 = 10x
5 x 2x = 10x
5 x 5 = 25
4x^2 + 20x + 25
So yes, the answer would be (2x + 5)(2x + 5)
