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.

⇒ 9x² – 3(a² + b²)x + 3(a² – b²)x – (a² + b²)(a² – b²) = 0

⇒ 3x(3x – (a² + b²)) + (a² – b²)(3x – (a² + b²)) = 0

⇒ (3x + a² – b²)(3x – (a² + b²) = 0

⇒ x