SOLUTION: If a rectangle with length L and width W has a perimeter of 4 cm, what are the definitions of the rectangle with the largest area and what is that area?

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Question 628179: If a rectangle with length L and width W has a perimeter of 4 cm, what are the definitions of the rectangle with the largest area and what is that area?
Found 2 solutions by dfrazzetto, josmiceli:
Answer by dfrazzetto(283) About Me  (Show Source):
You can put this solution on YOUR website!

Largest possible area of a rectangle is always a square, so L=W
4 = 4L = 4W; L = 1, W = 1
Length = Width = 1cm
Area = LxW = 1x1 = 1 cm^2

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The formula for perimeter is
+P+=+2L+%2B+2W+
given:
+P+=+4+ cm
+4+=+2L+%2B+2W+
+2+=+L+%2B+W+
+W+=+2+-+L+
------------
The formula for area is
+A+=+W%2AL+
By substitution:
+A+=+%28+2+-+L+%29%2AL+
+A+=+-L%5E2+%2B+2L+
This is a parabola with A plotted on the
vertical axis and +L+ on the horizontal.
The minus sign in front of +L%5E2+ means
the parabola has a maximum, not a minimum.
------------------------------------
If the equation has the form +f%28L%29+=+a%2AL%5E2+%2B+b%2AL+%2B+c+,
then the +L+ coordinate of the maximum is at
+-b%2F%282a%29+
+a+=+-1+
+b+=+2+
+L%5Bmax%5D+=+-2%2F%282%2A%28-1%29%29+
+L%5Bmax%5D+=+1+
So, the max is at ( 1,A ) where +A+ is
+A+=+-1%5E2+%2B+2%2A1+
+A+=+-1+%2B+2+
+A+=+1+
The maximum area is 1 cm2
and, if +L=1+, then
+W+=+2+-+L+
+W+=+2+-+1+
+W+=+1+
So the maximum area is when the rectangle is a square
with +L=W=1+