Posted by **manjula** on Tuesday, January 15, 2013 at 2:06am.

if (l1,m1,n1),(l2,m2,n2),(l3,m3,n3) are the direction cosines of three mutual perpendicular lines,show that the line whose direction ratios area l1+l2+l3,m1+m2+m3,n1+n2+n3 make equal angles with them

- analytical geometry -
**drwls**, Tuesday, January 15, 2013 at 3:11am
Because the first three lines are mutually perpendicular, dot products of pairs of lines are zero.

l1*l2+m1*m2+n1*n2 = 0

l2*l3+m2*m3+n2*n3 = 0

l1*l3+m1*m3+n1*n3 = 0

Finally, using the above equations, and another dot product, show that the cosine of the angle between the fourth vector and any of the first three vectors is the same.

- analytical geometry -
**DIPRA**, Monday, August 25, 2014 at 4:52am
listen to me dear.solve these six equations.l1l2+m1m2+n1n2=0,l2l3+m2m3+n2n3=0and l1l3+m1m3+n1n3=0...with these solve theselil2+m1m2+n1n2=l2l3+m2m3+n2n3=l1l3+m1m3+n1n3

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