David has 400 yards of fencing and wishes to enclose a rectangular area against a pre-existing fence. What is the maximum area that David can have?

A. 5000 yd^2
B. 10000 yd^2
C. 15000 yd^2
D. 20000 yd^2


Answer: D

Respuesta :

The maximum area that David can have is  10,000 yd^2

Area of a rectangle

The formula for calculating the area of a rectangle is expressed as:

A = lw

  • l is the length
  • w is the width

If David has 400 yards of fencing, then;

P = 2(l +w)

400 = 2( l+ w)

200 = l + w

l = 200 - w

Substitute into the area

A = (200-w)w

A = 200w - w^2

If the area is maximized, then;

dA/dw = 0
dA/dw = 200 - 2w

2w =200

w =  100 yards

Recall that;

200 = l + w

l = 200 - 100

l = 100

The maximum area = 100 * 100

The maximum area = 10,000 yd^2

The maximum area that David can have is  10,000 yd^2

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