# Hyperbolas and Asymptotes

1. Aug 12, 2006

How do u find the asymptotes to hyperbolas??

what are the asymptotes to this equation?

-x^2/4 + y^2/8 = 1

i really need help

2. Aug 12, 2006

### HallsofIvy

Staff Emeritus
Suppose x and y are very, very large. Then that "1" on the right hand side of
$$-\frac{x^2}{4}+ \frac{y^2}{8}= 1$$
is very very small compared to the other two terms so the equation is approximately
$$-\frac{x^2}{4}+ \frac{y^2}{8}= 0$$

Of course, $$-\frac{x^2}{4}+ \frac{y^2}{8}$$
factors as
$$(\frac{x}{2}+ \frac{y}{\sqrt{8}})(-\frac{x}{2}+\frac{y}{\sqrt{8}})$$
so for large x,y your equation is approximately
$$(\frac{x}{2}+\frac{y}{2\sqrt{2}})(-\frac{x}{2}+\frac{y}{2\sqrt{2}})= 0$$

Certainly if "ab= 0" then either a= 0 or b= 0. That gives you two linear equations whose graphs are close to the hyperbola for large x,y: the asymptotes.