Answer: (x²+y)(x²–3y)
Step-by-step explanation: The given expression is x⁴–2x²y–3y²
= x⁴ – (3-1)x²y – 3y²
= x⁴ – 3x²y +x²y –3y²
= x²(x²–3y) + y(x²–3y)
= (x²+y)(x²–3y)
