1, the coordinate of A B is (1-7,3-1,2-(-1)) = (-6,2,3), and the module AB=7 can be calculated according to the calculation formula of the module.

2. There are three direction cosines: direction cosines with X axis: cosa=x 1/ modulus AB=-6/7, direction cosines with Y axis: cosb=y 1/ modulus AB=2/7, and direction cosines with Z axis: COSR = Z 1.

3. There are also three orientation angles: the included angles (orientation angles) with the positive directions of X-axis, Y-axis and Z-axis are arccos(-6/7) respectively.

arccos2/7，arccos3/7