Simplify it first
(2x+5)^2 - 1
= (4x^2 + 20x + 25) - 1
= 4x^2 + 20x + 24
Use 4 [from the first term] and 24 [last term] as the basis for your factors;
4 has 1, 2, 4 as it's factors
24 has 1, 2, 3, 4, 6, 12, 21 as it's factors
Find the most apporpriate one- you can use Synthetic Division or simply "Trial and Error"
You will soon get
(4x + 12) (x + 2) as the factors
But remember; (4x + 12) can still be factored.
Divide it by 4...
(4x + 12) / 4 = (x + 3)
So yor factors are now
4 (x + 3) (x + 2)
