A rectangle has a perimeter of 80 cm. If its width is x, express its length and area in terms of x, and find the maximum area.
perimiter=2L+2W
w=x
P=80
80=2L+2x
diviide by 2
40=L+x
40-L=x
40-x=L
the area is found by legnth times width
LW or Lx
for a maximum area, try to get the legnths of the sides the same
therefor
L=W=x for max area
40=x+x
40=2x
divide 2
20=x
max area =legnth times width=20^2=400
note: all squares are rectangles, but not all rectangles are squares
L=40-x
A=(40-x)(x)
max area=400 cm^2
The maximum area will be "400 cm²"
Given:
Perimeter = 80 cm
then,
Length,
Area,
= \((40-x)x \ cm^2\)
For, Area to be maximum
→ \(\frac{dA}{dx} =0\)
→ \(\frac{d}{dx} (40-x)(x)=0\)
→ \(40-2x =0\)
→ \(2x =40\)
→ \(x = \frac{40}{2}\)
→ \(= 20\)
hence,
The maximum area,
= \((40-20)20\)
= \(20\times 20\)
= \(400 \ cm^2\)
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