Math CentralQuandaries & Queries


Question from Angela, a student:

A parabolic arch has an equation of x^2 + 20y - 400 = 0 where x is measured in feet. How do I find the maximum height of the arch?

Hi Angela,

A parabolic arch is symmetric around the line through its vertex.


P and Q are the points where the graph crosses the x-axis. Find the x-coordinates of P and Q and then find the point on the x-axis half way between them. The maximum height of the arch occurs at this point.


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