W=2L-5
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A=L*W
=L(2L-5)
=2L²-5L
-------------
dA/dL=4L-5
When dA/dL=0,
4L-5=0
4L=5
L=5/4
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When L=5/4
A=5/4*(2*(5/4)-5)
=5/4*(10/4-20/4)
=5/4*((-10)/4)
=5/4*(-5/2)
=-25/8
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*You may have been given a badly written out question. The answer doesn't make sense.