# Equations for tangent & normal at P2 of circle P1 P2 P3?

1. Apr 15, 2010

### CosmicVoyager

Greetings,

Given three points P1 P2 P3 on a circle in x,y,z coordinates, I am trying to figure out how to get the tangent and normal at P2.

Anyone?

Thanks

Last edited: Apr 15, 2010
2. Apr 15, 2010

### tiny-tim

Hi CosmicVoyager!

Well, that means you first need to find the centre of the circle …

what lines do you think that will be on?

3. Apr 15, 2010

### CosmicVoyager

The center of the circle won't be on any of the lines between the points. It is opposite the their normals?

4. Apr 15, 2010

### HallsofIvy

Staff Emeritus
If you construct the perpendicular bisectors of the lines between the points, they will intersect at the center of the circle.

Once you know that, construct the line from that center to each point. That line itself will be normal to the circle at the point. Constructing the line perpendicular to that line at the point gives you the tangent to the circle at that point.