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Point on a parabola where the tangent intersects a point

  1. Oct 19, 2009 #1
    1. A car is traveling on a highway shaped like a parabola with its vertex at the origin. The car begins at a point 100m west and 100m north of the origin and is traveling easterly. There is a statue 100m east and 50m north of the origin. At what point on the highway will the car`s headlights illuminate the statue.

    2. d/dx x^n = x*x^(n-1)

    3. The car begins at (-100,100) and travels on the domain [-100,inf).

    let f(x) represent the path of the car, thus f`(x) will represent the car`s headlights.

    f(x)=(1/100)*x^2 and f'(x)=(1/50)*x

    We need to find point P, who's tangent line intersects (100,50).

    Since the equation of the tangent is y=mx+b, and m=f'(x), then (50-y)/(100-x)=(1/50)x

    I then solved for y to recieve y=(x^2+100x+2500)/50

    and for y=0, x=50.

    So sub y=50 into my original eqn:

    Thus, 50=(1/100)*x^2 so, 50sqrt(2)=x

    And the statue will be illuminated by the car`s headlights when the car is at (50*sqrt(2), 50)?

    Does this look correct?
    Last edited: Oct 19, 2009
  2. jcsd
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