Question

- The length of a rectangle is 2 less than 5 times its width. The area of the rectangle is 39 km².

Find the length and width of the rectangle.

Answer 1

Length is 13 and width is 3

Explanation:

First find an equation that represents this situation.

39 = w * (5w-2)

This works because 39 (the total area) is w (the width) times 5w - 2 (the length). So solve for w.

39 = w * (5w-2)

First, distribute the w over the terms in parentheses

39 = 5w^2 - 2w

Then, subtract (5w^2 - 2w) from both sides.

39 - 5w^2 - 2w = 0

Factor the left side of the equation:

(−5w−13)(w−3)=0

Then set each factor equal to zero.

−5w−13 = 0

Add 13 to both sides, then divide both sides by -5 to isolate w. This leaves you with w = -13/5

Then the other factor:

w−3 = 0

Add 3 to both sides. You're left with w = 3.

So w is either -13/5, or 3. And since the width can't be negative, it is 3.

Now to find the height, plug 3 into the equation we had from earlier:

39 = w * (5w-2)

Substitute w into the equation:

39 = (3) * (5(3)-2)

39 = 3 * (15 - 2)

39 = 3 * (13)

Because 3 * 13 is equal, 13 is the length.