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 quad (12)/(13),(-3)/(13),(-4)/(13),(4)/(13),(12)/(13),(3)/(13);(3)/(13),(-4)/(13),(12)/(13) are mutually perpendicular.

(-4)/(13)+0=0+(-4)/(13)

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 .

(9)/(13)+(-8)/(13)+(4)/(3)+(-5)/(8)

(8)/(4)-(6)/(3)+(9)/(12)-:(15)/(13)

((12)/(17)times(12)/(17)-(13)/(34)times(13)/(34))/((12)/(17)+(13)/(34))

Solve : 4/(13)+2/(13)+1/(13)

(2/13)^(4/3)div(2/13)^(5/3)

Prove that: 2cos (pi)/(13) cos (9 pi)/(13)(3 pi)/(13)(5 pi)/(13)=0

13^(4/3)div13^(1/3)