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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