How do you find angle between two points when their co-ordinates are known?

Answer 1

The angle between 2 points is 180 degree if you draw a straight line through. If you mean the angle which it slants by, try think of it with a right-angled triangle. Suppose the points are A (1,1) and B (2,3) and you want to find the bearing of B from A (bearing is angle it slants by from a vertically upright line, clockwise). If you want, you can sketch it on a paper to visualize things.

1) Find a point where the two lines for A and B will meet perpendicularly and upright from A (1,3)

2) Find the length AC and BC (it should be straightforward; AC is 2 units, BC is 1 unit)

3) Put them in the expression tan-1 (O/A) where tan-1 is tangent inverse, O is the length of the opposite line (BC for this case), A is the length of the adjacent line (AC for this case). You should get tan-1 (2/1) or tan-1 2 which gives 63.4 degrees (to one significant figure).

4) From that answer, I can tell you that the bearing of B from A is 063.4o (the "0" is necessary for bearings which has a fixed format of ***.* where * represents a number). You can also say that the line is tilted 26.6o upwards from a flat line.

Depending on question, you may need to alter this method slightly but this is one method that will work efficiently (when you can visualize it without drawing, it does get quite fast)