math
posted by Mary on .
Kira has feet of fencing. She will use it to form three sides of a rectangular garden. The fourth side will be along a house and will not need fencing. For the area of the garden to be the maximum, how long should the side opposite the house be?

You failed to indicate how many feet of fencing Kira has.

let the perimeter be P, where P is a constant
let the length be y and the width be x
2x + y = P
y = P  2x
Area = xy
= x(P2x)  Px  2x^2
d(area)/dx = P  4x
= 0 for a maximum area
4x = P
x = P/4
y = P  P/2 = P/2
So the long side should be half the perimeter, and the short side whould be a quarter of the perimeter. 
i need help with my math homework

if the perimeter of a rectangle is 184cm and the width is 39cm calculate its length