100cm2

i.e

40 = 2(l+w)

l+w =20

l=20-w...........(1)

A = lw

= (20-w)w

=20w-w2

dA/dw =20 -2w

but at maximum A, dA/dw = 0

so 20-2w=0

w=10

which means l=20-10=10

so Area = 10*10=100cm2

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A rectangle has perimeter equal to 40cm. What is the maximum possible area of this rectangle?

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