# Hyperbola and an ellipse to intersect orthogonally?

1. Oct 27, 2010

### zorro

What is the condition for a hyperbola and an ellipse to intersect orthogonally?
I have a formula for orthogonal circles -> 2g1g2 + 2f1f2 - c1c2 = 0

2. Oct 28, 2010

### Petr Mugver

Re: Orthogonality

1) Write down the equations of the two curves.

2) Find the intersections by solving the two equations simultaneously.

3) Consider one of theese intersections, say (x0, y0).

4) Derive the first equation with respect to x and y. You get a vector u(x ,y) (the gradient).

5) Do the same with the second equation. Call the gradient v(x, y).

6) Evaluate u and v at the point (x0, y0) calculated earlier.

7) Calculate the scalar product u.v and impose it's zero.

3. Oct 28, 2010

### zorro

Re: Orthogonality

How do you apply rule 2 if you don't know the equation of one of the curves?
Consider this question-

An ellipse intersects the hyperbola 2x2 - 2y2 = 1 orthogonally. The eccentricity of the ellipse is reciprocal of that of the hyperbola. If the axes of the ellipse are along the co-ordinate axes, then find the equation of the ellipse.

Eccentricity of the ellipse is 1/√2

The relation betwen a and b of ellipse is a2 = 2b2

Now how do you proceed?

4. Oct 28, 2010

### Petr Mugver

Re: Orthogonality

Well if what you say is correct (I didn't check it) then the two equations are:

x^2 - y^2 = 1/2

x^2 + 2y^2 = 2b^2

Try doing steps 2) - 7) with theese, you should get a constraint for the free parameter b.