Chapter 9 Quadratic Relations and Conic Sections - 9.2 Graph and Write Equations of Parabolas - 9.2 Exercises - Problem Solving - Page 625: 59a

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The cross section has the equation $x^2= 10.5y$ Since the depth of the searchlight is 9.5 inches, we can write $y=9.5$ Substitute: $x^2=10.5(9.5)=99.75$ Thus, $x=\pm \sqrt 99.75\approx \pm10$ The width of light projected from the searchlight’s reflector is $\approx 20$ inches.