How do I determine three points are collinear? Using the Vector equation of a line?
A (3, -8) B(5/2, 6) and C(-1/2, 90)

Question

How do I determine three points are collinear? Using  the Vector equation of a line? 
A (3, -8) B(5/2, 6) and C(-1/2, 90)

jamesj · Answer

If three points A B and C are collinear, then the cross product of the vectors AB and BC will be zero.

jamesj · Answer

Or in other words, AB will be a scalar multiple of BC.

anonymous · Answer

@JamesJ A, B, and C are not vectors. They are points

anonymous · Answer

AB vector=BC vector ?

jamesj · Answer

Or in other words, the direction vector of line through A and B, and the direction vector through B and C, will be the same up to a constant multiple.

Yes, I know that.  But you can define a vector AB = B - A where you now consider A and B to vectors in the obvious, canonical way.

anonymous · Answer

a straight line with 180 degree

anonymous · Answer

That helps. I had another question @JamesJ about vectors. When you subtract two vectors, how do you know which way to draw the arrow when drawing an illustration representing the subtraction? ie|dw:1335420263066:dw|