Answer:
80000 square meters
Step-by-step explanation:
perimeter + dividing fence = 800
let a = length
let b = width
let c = length of dividing fence
perimeter = 2*a + 2*b
let's say...
c is the same as the length
2a + 2b + c = 800
2a + 2b + a = 800
3a + 2b = 800
area = length*width
area = a*b
area / b = a
3*(area/b) + 2b = 800
3*(area/b) = 800 - 2b
area/b = (800 - 2b)
area = (800 - 2b)*b
To make the area large, we make the right hand side large.
800b - 2b^2
If you put in terms of x, y it looks like a downward opening parabola, so the max area is at the vertex. Half way between the roots.
y = -2x^2 + 800x
y = -x^2 + 400x
0 = x*(-x + 400)
roots are x= 0 and x = 400
vertex is at x, aka b = 200
area at b=200 is (800 - 400)*200 = 80000
and a is area/b... 80000/400 = 200
