The area of a rectangle is expressed as x4 - 9y2. What are the possible dimensions of the rectangle?

This is a stupid question.  The teacher who asked this needs to go back to school.

A = x⁴ - 9y²

That's going to be a number.  As long as it's positive we can choose any length for our rectangle L and we can compute the width by W=A/L.   So the correct answer is the dimensions are L by  (x⁴ - 9y²)/L.

They don't want the correct answer.  They want you to factor this expression.  We'll do it, but don't believe for a second this factoring somehow constrains the possible dimensions of some rectangle.

We use the difference of two squares, a²-b² = (a+b)(a-b)

A = x⁴ - 9y² = (x²)² - (3y)² = (x²+3y)(x²-3y)

x²+3y  by  x²-3y

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