A reflective telescope contains a mirror with a parabolic shape of revolution. I

Question

A reflective telescope contains a mirror with a parabolic shape of revolution. If the mirror is 18 inches across at its opening and is 3 feet deep, find where the light will concentrate.

Un telescopio reflectivo contiene un espejo con forma de paraboloide de revolucion. Si el espejo es 18 pulgadas a través en su abertura y es 3 pies de profundidad, halla donde se concentrara la luz 0.7 pulgadas desde el vértice O 0.6 pulgadas desde el vértice 6.8 pulgadas desde el vértice O 0.3 pulgadas desde el vértice

Explanation / Answer

x^2 = 4ay

If the mirror is 18 inches across at its opening and is 3 feet deep

3ft = 36 inches

we have a point on the parabola as : (9, 36)

So, x^2 = 4ay ; 81 = 4*a*36

a = 81/4*36 = 9/4*4 = 9/16 = 0.5625 inches from the vertex

Option B 0.6 inches

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