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