SOLUTION: The perimeter of a rectangle is 80 feet. Express its area, A as a function of the length x of a side.

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Question 1043662: The perimeter of a rectangle is 80 feet. Express its area, A as a function of the length x of a side.
Answer by ikleyn(52880) About Me  (Show Source):
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Let L be the length of the rectangle, and W be the width.


Then L + W + L + W = P, perimeter, or  2*(L+W) = P,  or  L + W = P%2F2 = 80%2F2 = 40 feet.

Hence, W = 40 -L.

The area of the rectangle is equal to 

A = L*W = L*(40-L) = 40L+-+L%5E2.

So, A = 40L+-+L%5E2 expresses the area of the rectangle as the function of L.

Solved.

You can find many simple solved introductory problems on area of rectangle in the lesson
    - Problems on the area and the dimensions of a rectangle
in this site.