You may want to review equations of ellipses first.
Equations of hyperbolas look like −4x2 + y2 − 16 = 0. (Note that one of the coefficients is negative; that's what makes it a hyperbola instead of an ellipse.) As with ellipses, we'll start with hyperbolas centered at the origin. Also just like ellipses, we start by dividing both sides by 16, so it becomes −1 ⁄ 4 * x2 + 1 ⁄ 16 * y2 − 1. The minus sign is in front of the x2 term, so the hyperbola is horizontal. (What a hyperbola looks like is hard to describe; ideally your teacher will draw you a pictures of both a horizontal and a vertical hyperbola.) So then we look at the y2 term to find the radius, which comes out to 16, the square root of 4. (If it were vertical, then we'd get the radius from the x2 term. Also, on this site, there's a check box for horizontal. If it's vertical, then just leave it unchecked.)
Unlike ellipses, hyperbolas have only one radius. They do, however, have something that I'll call the asymptotic slope. (To see what this means geometrically, you'll want to look at a picture.) To find it, divide the coefficient of x2 by the coefficient of y2, ignoring signs. Here, that means you get 4 / 1 = 4. Then, you take the square root, getting 2, the answer.