math

The equation
4x^2 +9y^2 -36 = 0
represents an ellipse in standard position.
Find the coordinates of the foci and the equations of the directrices.
The Foci are (+-f, 0) where f>0
I have worked out f=sqrt(5)

not sure how to work out the directrices (d)

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asked by s17
  1. In standard form,

    x^2/9 + y^2/4 = 1

    a = 3
    b = 2
    c = √5

    You are correct that the foci are at (±√5,0)

    The directrices are at x = ±a^2/c = ±9/√5

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    posted by Steve

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