SOLUTION: the perimeter of a rectangle is fixed at 20 cm. if the length l is increasing at the rate of 1 cm/s, for what value of l does the area of rectangle start to decrease?

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Question 985685: the perimeter of a rectangle is fixed at 20 cm. if the length l is increasing at the rate of 1 cm/s, for what value of l does the area of rectangle start to decrease?
Answer by Alan3354(69443) About Me  (Show Source):
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the perimeter of a rectangle is fixed at 20 cm. if the length l is increasing at the rate of 1 cm/s, for what value of l does the area of rectangle start to decrease?
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The max area of a rectangle of fixed perimeter is a square.
--> starts to decrease at L = 5 cm