Question 934848
proceed with your description and you will find the park is 100 meters on a side, as a square region.  This is a very common exercise question.  


Let x be the side of one dimension and y be the side of the other dimension.  xy=the area, and 2x+2y=400.
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{{{A=xy}}}, for area.
{{{x+y=200}}}, simplified perimeter.
You want A as a formula with just a single variable; A as a function of the one variable.