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.

⇒ 4(25 + x² + 10x) – 4(25 + x² – 10x) = 15(25 – x²)

⇒ 15x² + 80x – 375 = 0

⇒ 3x² + 16x – 75 = 0

⇒ 3x² + 25x – 9x – 75 = 0

⇒ x(3x + 25) – 3(3x + 25) = 0

⇒ (x – 3)(3x + 25) = 0

⇒ x = 3, - 25/3