The third angle would measure 90 degrees
Perimeter (P) = 2 · Length(L) + 2 · Width (W) → P = 2L + 2W
Solve for either L or W (I am solving for L).
200 - 2W = 2L
(200 - 2W)/2 = L
100 - W = L
Area (A) = Length (L) · Width (W)
= (100 - W) · W
= 100W - W²
Find the derivative, set it equal to 0, and solve:
dA/dW = 100 - 2W
0 = 100 - 2W
W = 50
refer to the equation above for L:
100 - W = L
100 - 50 = L
50 = L
Dimensions for the maximum Area are 50 ft x 50 ft
The answer would be 212,I can't completely explain why because I did it the long way which took me over an hour to do.
Diagonal = √50² + 40² = √2500+1600 = √3900 = 10√39 miles