Answer:

A. 400 m2

Explanation

intion: suppose the side lengths of the rectangular are x and y.

• 2(x+y) = 80 ⇒ y = 40-X

the area of rectangular : 2 = xy = X

• 1 = X(40-x) = 40X-X²

• 7² = 40-2X=0 ⇒ x = 20 = 7 = 40×20-70³² = 400 m²

• {Z=40X-X²³² ⇒ when the first derivative is 0, the corresponding

• Z value is the maximum I

So when x 25 zom, z is maximum

So choose A

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