In factorization, we write the middle term of the quadratic equation either as a sum of two numbers or difference of two numbers such that the equation can be factorized.

⇒ 25x² + 25x + 4 = 0

⇒ 25x² + 20x + 5x + 4 = 0

⇒ 5x(5x + 4) + (5x + 4) = 0

⇒ (5x + 1)(5x + 4) = 0

⇒ x = -1/5, -4/5