Conic Sections and Foci of Ellipses

We're just learning about ellipses and conics, and I'm a bit confused with ellipses, parabolas, circles, and hyperbolas, so a little help with this sample problem would be great.

In which of the following equations would the ellipse have foci on the y-axis, the x-axis, or neither?

$1=\frac{x^2}{9}+\frac{y^2}{16}$

$1=\frac{x^2}{9}+\frac{y^2}{4}$

I tried graphing these already, but I'm still not exactly sure where the foci lies. In fact, what does each number in the equation of an ellipse represent? I apologize for the very ignorant questions, but we just started learning about conics. :)

• One may speak of where a focus lies, or of where the two foci lie, but not of "where the foci lies". "Foci" is the plural of "focus". ${}\qquad{}$ – Michael Hardy Dec 23 '14 at 21:20
• I apologize for the misuse of words. Thank you for the correction. – user202767 Dec 23 '14 at 21:21

• In the first case above they're on the $y$-axis; in the second on the $x$-axis. ${}\qquad{}$ – Michael Hardy Dec 23 '14 at 21:25