SOLUTION: A rectangle has a perimeter of 80 cm. If its width is x, express its length and its area in terms of x. What is the maximum area of the rectangle?

Question 434436: A rectangle has a perimeter of 80 cm. If its width is x, express its length and its area in terms of x. What is the maximum area of the rectangle?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
y^2-4y-45 = 0
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I'm not sure what method your teacher used.
Your problem is factorable as follows.
This is sometimes called inverse-FOIL.
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y^2-9y+5y-45 = 0
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Factor the 1st 2 and the last 2 terms separately:
y(y-9)+5(y-9) = 0
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Factor again:
(y-9)(y+5) = 0
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Solve:
y = 9 or y = -5
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Cheers,
Stan H.
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