Let x = length and y = width
You would have 2 lengths, so 2x and 3 widths, so 3y
Those need to equal total length of fence:
2x + 3y = 1200
The 3 widths would equal total fence minus the 2 lengths:
3Y = 1200-2x
Solve for y: y = 400 -2/3x
Area = length x width = xy. Replace y :
Area = x(400-2/3x) = 400x-2/3x^2
Differentiate:
400-4x/3 =0
4x/3 = 400
4x = 1200
X = 300
Y = 400-2/3(300) = 200
The dimension would be 300 ft x 200 ft
