Question

What expression represents the length of the rectangle?

Answer 1

9 + x

Explanation:

81 - x² ← is a difference of squares which factors in general as

a² - b² = (a - b)(a + b), thus

81 - x²

= 9² - x² = (9 - x)(9 + x)

Area = length × width = 81 - x² = (9 - x)(9 + x)

Since width = 9 - x then length = 9 + x