By definition, the number
is the ratio between the circumference and the diameter:

This implies that

And so your circumference is 
Here it is given that the width is x ft and total length of the fence is 2400 ft .
Let the length be y ft
So we have

Let A represents area, and area is the product of length and width .
So we get

Substituting the value of y, we will get

Second part
The area is maximum at the vertex, and vertex is

And

And that's the required dimensions .
Answer:
Step-by-step explanation:
f(x) = 2x^3 - 4x.....find f(-2).....so sub in -2 for x
f(-2) = 2(-2^3) - 4(-2)
f(-2) = 2(-8) + 8
f(-2) = -16 + 8
f(-2) = -8 <==