`13-(12-6-:3)`

[(2/13)^(-6)-:(2/12)^(3)]^(3)xx(2/13)^(-9)= ______________

Show that the three lines with direction cosines quad (12)/(13),(-3)/(13),(-4)/(13),(4)/(13),(12)/(13),(3)/(13);(3)/(13),(-4)/(13),(12)/(13) are mutually perpendicular.

Show that the three lines with direction cosines (12)/(13),(-3)/(13),(-4)/(13);4/(13);(12)/(13),3/(13);3/(13),(-4)/(13),(12)/(13) are mutually perpendicular.

Show that the three lines with direction cosines (12)/(13),(-3)/(13),(-4)/(13),4/(13),(12)/(13),3/(13);3/(13),(-4)/(13),(12)/(13) are mutually perpendicular.

Show that the three lines with direction cosines (12)/(13),(-3)/(13),(-4)/(13);4/(13);(12)/(13),3/(13);3/(13),(-4)/(13),(12)/(13) are mutually perpendicular.

A=[[1,3,-12,2,-13,0,-1]] and B=[[-2,3,-1-1,2,-1-6,9,-4]]

Show that the lines with direction cosines ((12)/(13),(-3)/(13),(-4)/(13))and((4)/(13),(12)/(13),(3)/(13)) are perpendicular to each other.

Show that the three lines with direction cosines (12)/(13),(-3)/(13),(-4)/(13),(12)/(13),(3)/(13),(-4)/(13),(12)/(13) are mutually perpendicular.

I : If OP = 21 and d.c.'s of vec(OP) are (2/7, 6/7, -3/7) then P = (6, 18, -9). II : If P = (3, 4, -12) then d.c.'s of vec(OP) are (3/13, 4/13, -12/13)

The value of |(11,12,13),(12,13,14),(13,14,15)| , is