Math CentralQuandaries & Queries


Question from Angela, a student:

The length of a rectangle is 6 inches less than 3 times its width. Find the
dimensions of the rectangle if its area is 45 square inches.

I know that A = lw, so if width is w, length is 3w-6. My set-up equation
is therefore: 45 = w(3w-6). So 3w squared-6w=45, which leads to a
quadratic equation, which is what gives me a funky answer. Help! :)

Hi Angela,

I agree with your solution so far and I don't see anything funky with the answer it gives. You have

3w2 - 6w = 45


3w2 - 6w - 45 =0

Dividing by 3 I get

w2 - 2w - 15 =0

Solve for w,

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