" (iv) "(3)/(13)

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.

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.

((13)^(3)+7^(3))/((13)^(2)+7^(2)-?)=20

Check if lines with direction-cosines : lt (12)/(13) , - (3)/(13) , - (4)/(13) gt , lt (4)/(13) , (12)/(13), (3)/(13) gt , lt (3)/(13) , (4)/(13) , (12)/(13) gt are mutually perpendicular .