SOLUTION: a jogging path is in the shape of an ellipse. if it is 100ft long and 50ft wide, what is the width of the track 20ft from either vertex

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Question 1198497: a jogging path is in the shape of an ellipse. if it is 100ft long and 50ft wide, what is the width of the track 20ft from either vertex
Answer by ikleyn(52886) About Me  (Show Source):
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a jogging path is in the shape of an ellipse.
if it is 100ft long and 50ft wide, what is the width of the track 20ft from either vertex
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Major semi-axis is a = 100/2 = 50 ft long.

Minor semi-axis is b =  50/2 = 25 ft long.


The equation of the ellipse is

    x%5E2%2F50%5E2 + y%5E2%2F25%5E2  = 1.


20 ft from the vertex is x= 50-20 = 30 ft from the center at the major semi-axis.


Substitute x= 30 into equation

    30%5E2%2F50%5E2 + y%5E2%2F25%5E2 = 1,

or

    y%5E2%2F25%5E2 = 1 - 30%5E2%2F50%5E2 = 1 - %283%2F5%29%5E2 = 1 - 9%2F25 = 16%2F25.


Hence,  y%2F25 = +/- sqrt%2816%2F25%29 = +/- 4%2F5.


It implies  y = +/- 25%2A%284%2F5%29 = +/- 20.


It means that the width of the track is 20 + 20 = 40 ft there.    ANSWER

Solved.