The management of the UNICO department store has decided to enclose a 855 ft2 area outside the building for displaying potted plants and flowers. One side will be formed by the external wall of the store, two sides will be constructed of pine boards, and the fourth side will be made of galvanized steel fencing. If the pine board fencing costs $2/running foot and the steel fencing costs $5/running foot, determine the dimensions of the enclosure that can be erected at minimum cost. (Round your answers to one decimal place.)
wood side ft
steel side ft
Let
x = side length of pine
y = side length of steel
so given the area,
xy = 855
The cost is now
c = 2*2x + 5y = 4x + 4275/x
dc/dx = 4 - 4275/x^2
Now just find where dc/dx = 0