SOLUTION: A flashlight is shaped like a paraboloid and the light source is placed at the focus so that the light bounces off parallel to axis of symmetry; this is done to minimize illuminati

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Question 1041774: A flashlight is shaped like a paraboloid and the light source is placed at the focus so that the light bounces off parallel to axis of symmetry; this is done to minimize illumination. A particular flashlight has its light source located 1 cm. from the base and is 6 cm. deep. What is the width of the flashlight's opening?
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
What I say here is help, but is not a complete answer.

The "base" would be the vertex for a parabolic cross section. Imagine or sketch a parabola concave upward with vertex at the origin (0,0), and focus at (0,1). There is a directrix which should be understood to be (0,-1).

Are you familiar with how to derive the equation for a parabola if the focus and directrix are given as known? If you know how, then find this equation. Use it to find the unknown coordinate of the point on the parabola, (u,6). Recall from the description, the flashlight is 6 cm deep. The width at the opening will be 2u.