Deriving an angle from three points

[Mark Swindell]

On Dec 15, 2009, at 10:35 PM, Mark Wieder wrote:

> Mark-
> 
> Tuesday, December 15, 2009, 10:21:47 PM, you wrote:
> 
>> 40,116
>> 98,186
>> 132,118
> 
>> How would one determine the angle created from three points, such as those above?
> 
> There are three angles. Which one are you interested in?
> 
> — 

The above represents roughly a V shape with the center point the vertex.  I was trying to detemine the internal angle.