# circles

- A CIRCLE is a perpendicular relationship between two points

In other words, A CIRCLE is a rotation of one point about the other.

Lines are "straight-forward" to consider. Circles just take you around and around.

like lines, circles are instantiated with twp points
Unlike lines, the two points are not interchangeable
one is defined and the **center point**, the other as the **radius point**

we use these points to derive the equation

`(x - h)^2 + (y - k)^2 + r^2 = 0`

```
// x offest
this.h = centerPoint.x;
// y offset
this.k = centerPoint.y;
//get radius length
this.r = centerPoint.distanceTo(radiusPoint);
// generate equation for circle
// (x - h)^2 + (y - k)^2 + r^2
this.eq = Algebrite.run( `clearall
(x - (${this.h}))^2 + (y - (${this.k}))^2 - (${this.r})^2` );
// log(" eq: " + this.eq);
```

right now - the circle does not have the equivalent of a xRoot or yRoot expression in the object this work is done in the intersection calculation

fairly straightforward until we get to the intersections