Question

What is the completely factored form of x4y – 4x2y – 5y?

y(x2 – 5)(x2 + 1)

y(x2 + 5)(x2 – 1)

(x2y – 5)(x2 + 1)

(x2y + 5)(x2 – 1)

Answer 1

Factor out y: y(x^4 − 4x^2 − 5). Let u = x^2: u^2 − 4u − 5 = (u − 5)(u + 1). Back-substitute u = x^2 to get y(x^2 − 5)(x^2 + 1).