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Can someone help me with with this function word problem?

Creative Landscaping has 60yd of fencing with which to enclose a rectangular flower garden. If the garden is x yards long, express the garden’s area as a function of the length. I know the answer is A(x)=30x-x^2 But I have no idea how to get it. Can someone explain it?

Details:

  1. let the garden be a x * y area you know that x+y+x+y = 60yd => 2x+2y=60=> 2y=60-2x=> y=30-x the area is A = x*y , replace y: A(x)=x*(30-x)=> A(x)=30x-x^2 EDIT: this is what the garden look like: ..._____x_____ ...|..................| y |..................| y ...|__________| .............x
  2. The length is x. There are two sides of length x so that uses up 2x yards of fencing. That leaves 60-2x yards of fencing. So the width of the rectangle is ½(60-2x) = 30-x yards. We find the area by multiplying the length by the width: x(30-x). Multiply out the brackets to get 30x-x². I hope this helps.