Determine cornertype based on xy values

Hello everyone,

I am trying to use excel for a geometrical automated calculation.
One of the steps that is needed in my calculation is to determine the type of corner. (Inner corner or outer corner)
The X and Y vaues are stored in an chronological list. Each datapoint got a separate column and X and Y values are split up in 2 rows.

I have a dilemma here, and I don't know if excel can handle this in an easy way:
innerouter.png

Let's assume you have three datapoints oriënted in the following way for both an inner (redand an outer corner:
x1 < x2 < x3
y1 > y2 > y3
(see above image)

In that case the location of the points by themselves are not enough to determine the type of corner.
So I assume I need to draw an imaginary line between point 1 and 3 (white line), in other words: is there a formula to make a function outof data point 1 + 3 and tell if datapoint 2 is left or right from this function?

Or maybe you have another solution?

Thank you very much for looking into this!