Answer:

Step-by-step explanation:
GIVEN: A fence is to be built to enclose a rectangular area of
square feet. The fence along three sides is to be made of material that costs
dollars per foot, and the material for the fourth side costs
dollars per foot.
TO FIND: Find the dimensions of the enclosure that is most economical to construct.
SOLUTION:
Area of rectangular fence 
let the length of fence 
let the width of fence 
let
be the smaller side
Area of rectangular fence enclosure 


cost of fence along three sides 
cost of fence along fourth side 
length of fence 
cost of fence building 

putting value of 


to find minimum value differentiating the equation





Hence the dimensions of the enclosure that is most economical to construct are
and 