A rectangular field is to be fenced on three sides with 1000 m of fencing. The fourth side is a straight river's edge that will not be fenced. Find the dimensions of the field so that the area of the enclosure is 120000 square meters.

Respuesta :

Answer:

[tex]300m\times 400m[/tex] or[tex]200m\times 600m[/tex]

Step-by-step explanation:

We are given that

Fencing used on three sides=1000 m

Area of field enclosure=120000 square meters

Let x be the length and y be the width of rectangle.

Fencing used on three sides=2x+y

[tex]2x+y=1000[/tex]

[tex]y=1000-2x[/tex]

Area of  field=[tex]xy=x(1000-2x)[/tex]

[tex]-2x^2+1000x=120000[/tex]

[tex]-x^2+500x=60000[/tex]

[tex]x^2-500x+60000=0[/tex]

Using quadratic formula

[tex]x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}[/tex]

[tex]x=\frac{500\pm\sqrt{(500)^2-4(60000)}}{2}[/tex]

[tex]x=\frac{500\pm 100}{2}[/tex]

[tex]x=\frac{500+100}{2}=300m[/tex]

[tex]x=\frac{500-100}{2}=200 m[/tex]

[tex]y=1000-2(300)=400 m[/tex]

[tex]y=1000-2(200)=600m[/tex]

Dimension of the field

[tex]300m\times 400m[/tex] or[tex]200m\times 600m[/tex]

Answer:

length = 500 m , width = 250 m

Step-by-step explanation:

Let the length of the field is L and the width is W.

Area of the field , A = 120000 sq. metre

Length of fencing = 1000 m

Total length of fence = L + 2 W = 1000

L = 1000 - 2 W

Area = Length x width

A = L x W

A = (1000 - 2W) x W

A = 1000 W - 2 W²

for mxima and minima,

dA/dW = 0

1000 - 4W = 0

W = 250 m

L = 1000 - 2 x 250 = 500 m

Thus, the length of the field is 500 m and the width of the field is 250 m.

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