Question 1160971
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The parabolic surface measures 120 cm in diameter at the top and is 20 cm deep at its center. How far from the vertex should the microphone be​ located?
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Putting vertex at (0,0) and two points  (-60,20) and (60,20),
{{{y=ax^2}}}
{{{20*a*60^2}}}
{{{a=1/180}}}
-
{{{180y=x^2}}}


Focus is d cm from vertex.
{{{4d=180}}}
{{{d=180/4}}}
{{{highlight(d=45)}}}{{{cm}}} from vertex