`4/13+9/13+2/13=-/13`

3/13-2/13+5/13 =

3/13+7/13+1/13

5/13-5/13 =

Work out the following : 7/13+2/13-5/13

7/13+(-9)/13=(__+(-9))/13=-/13

13/5-5/13 =

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

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.

If [(2+x,3,4),(1,-1,2),(x,1,-5)] is a singular matrix then x is (A) 13/25 (B) -25/13 (C) 5/13 (D) 25/13