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A satellite dish is shaped like a paraboloid of revolution. This means that it can be formed by rotating a parabola around its axis of symmetry. The receiver is to be located at the focus. If the dish is 84 feet across at its opening and 7 feet deep at its center, where should the receiver be placed?

NASA’s Deep Space Network antenna, Deep Space Station 35 (DSS-35) in Canberra, Australia public domain nasa.gov
nasa.gov

Find the equation of the parabola.  

How far above the vertex should the receiver be placed?