# Homework Help: Eliminating the parameter

1. Feb 24, 2010

### jcook735

Express the set of parametric equations x = E^t + e^-t and y = e^t - e^-t without using the parameter t.

I really have no idea how to do this one. I tried substituting, and it just turned into a jumbled mess of nothing. Please help

2. Feb 24, 2010

### Roni1985

did you try squaring the x and the y equations ?

3. Feb 24, 2010

### jcook735

well I got x^2 = e^2t + 2 + e^-2t and y^2 = e^2t - 2 + e^-2t but I dont know where to go from there

4. Feb 24, 2010

### Roni1985

if you move the 2's to the other side, your right hand sides are basically equal.

5. Feb 24, 2010

### jcook735

OH!!! Thanks! So if I understand correctly, ill move the twos over and get the right sides to be the same and x^2 - 2 and y^2 +2. Then I should set these two equal to each other and find y, which comes out to be (plus or minus) the square root of x^2 - 4?

6. Feb 24, 2010

### Roni1985

I think you need to take only the 'plus', because if I'm not mistaken, Y can't be negative according to the parametric equations.
So the range is Y=>0.