Question

The width of a rectangle is 1 units less than the length. The area of the rectangle is 72 units. What is the width, in units, of the rectangle?

Answer 1

A = l × w. Substitute 72 into A and fill in the rest of the equation.

w = l - 1. Plug l - 1 into w

72 = l × (l - 1). Multiply l by (l - 1)

72 = l^2 - l. Subtract 72 from each side.

0 = l^2 - l - 72. Factor.

0 = (l + 8) (l - 9). Set each term equal to zero.

(l + 8) = 0. Subtract 8 from each side.

l = -8. Length cant be a negative number so let's try the other term.

(l - 9) = 0. Add 9 to each side.

l = 9. The length is 9.

Earlier we stated that the width is one less than the length, therefore, the width is 9 - 1 = 8.

The width is 8 units.