Answer:
Breadth = 60, Length = 60
Step-by-step explanation
Let length & breadth of rectangular area be : L & B
As, Fencing Yards = 320. So, perimeter ie 2 (L + B) = 320
B = (320 - 2L)/2 → B = 160 - L (*)
Area of rectangle [A] = L x B = L (160 - L) → A = 160L - L^2
Maximising Area, So first derivative d [A] / d [L] = 160 - 2L
d [A] / d [L] ] = 0 → 160 - 2L = 0 → L = 160/2 → L = 80
By (*) : B = 160 - L = 160 - 80 → B = 80
Checking maximising condition, double derivative d^2[A] / d[L]^2 = -2
As d^2[A] / d[L]^2 is negative, L & B values are maximising A
