Distance of the Focus of an Hyperbola to the X-Axis For a National Board Exam Review:


  How far from the $x$-axis is the focus of the hyperbola $x^2 -2y^2 + 4x + 4y + 4$?


Answer is $2.73$

Simplify into Standard Form:

$$ \frac{ (y-1)^2 }{} - \frac{ (x+2)^2 }{-2} = 1$$

$$ a^2 = 1 $$
$$ b^2 = 2 $$
$$ c^2 = 5 $$

Hyperbola is Vertical: 

$$ C(-2,1) ; y = 1 $$

$$ y = 1 + \sqrt5 = 3.24 $$
$$ y = 1 - \sqrt5 = 1.24 $$

Both answers don't match; What am I doing wrong?
Please check the formulas as you have two foci. $x^2 - 4x - 4 - 2y^2 - 4y = 0\to (x-2)^2 -2(y+1)^2 =6 \to \dfrac{(x-2)^2}{(\sqrt{6})^2}-\dfrac{(y+1)^2}{(\sqrt{3})^2}=1\to a = \sqrt{6}, b = \sqrt{3}\to c = \sqrt{6+3} = 3\to F= (2\pm 3,-1)=(-1,-1), (5,-1)\to \text{ distance to x-axix = 1}$
$\frac{(x + 2)^2}{2} - \frac{(y - 1)^2}{1}; C = (-2, 1)$

$C = \sqrt{2 + 1} = \sqrt{3}$

Answer: $1 + \sqrt(3) = 2.73$