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

First factor out the common factor y: x⁴y − 4x²y − 5y = y(x⁴ − 4x² − 5). Treat x² as a single variable; the quadratic factors as (x² − 5)(x² + 1), since the factors multiply to −5 and add to −4. So the completely factored form is y(x² − 5)(x² + 1), choice A.

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