Posted by Abbey(Please help) 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  Reiny, 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(x2)^2 + 4(y+1)^2 = 9
(x2)^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  Anonymous, Tuesday, August 28, 2012 at 7:07pm
9^2[(4.2x3.4)9.28