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Posted by on Monday, May 3, 2010 at 1:49pm.

Find the center, vertices, foci, and eccentricity of the ellipse.

9x^2 + 4y^2 - 36x + 8y + 31 = 0

My answer was:
center=(2,1)
v=(-2,10)(-2,-10)
f=(-2,11)(-2,-11)
e=11/3

Where did I make a mistake?

  • Math - , Monday, May 3, 2010 at 3:56pm

    9x^2 + 4y^2 - 36x + 8y + 31 = 0
    9(x^2 - 4x + ...) + 4(y^2 + 2y + ...) = -31
    9(x^2 - 4x + 4) + 4(y^2 + 2y + 1) = -31+36+4
    9(x-2)^2 + 4(y+1)^2 = 9
    (x-2)^2 + (y+1)^2 /(9/4) = 1

    my centre is (2,-1)
    a^2 = 1
    b^2 = 9/4) etc

    have you found your error?

  • Math - , Tuesday, August 28, 2012 at 7:07pm

    9^2-[(4.2x3.4)-9.28

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