One step in the Graham scan algorithm is to determine the direction of turns. Suppose you have 3 points – a, b and c. If you look at the angle formed by two lines ab and bc, you can find it can turns...

One step in the Graham scan algorithm is to determine the direction of turns. Suppose you have 3 points – a, b and c. If you look at the angle formed by two lines ab and bc, you can find it can turns left (counter-clockwise), turns right (clockwise), or form a straight line. How do you determine the direction?