# Linear Algebra: Denoting an interval

1. May 25, 2010

### Niles

1. The problem statement, all variables and given/known data
Hi

I have a position given by the point a vector v points to. Now I have a function, which is only defined for the points on and inside a circle with radius 2 within this point. Can I write this interval as

$$x,y \in [(x-v_x)^2-(y-v_y)^2=4]$$

?

Best,
Niles.

2. May 25, 2010

### Staff: Mentor

The domain of definition is not an interval, which is a segment of a line. The domain is a circular disk of radius 2, centered at the point (vx, vy). You would write the domain as
$$D = \{(x, y) | (x - v_x)^2 + (y - v_y)^2 \leq 4 \}$$