Question 891963
Let the two parallel sides have length of x meters each.  Then the third remaining side has length 100 - 2x meters.  The area would then be A(x) = x(100 - 2x).  The graph of this is a parabola facing downward, with x-intercepts at x = 0 and x = 50.  The highest point (vertex) would then be situated where x = 25, midway between the two x-intercepts (roots).  The largest area would then be 25* 50 = 1250 square meters.