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# If the direction cosines of two lines are such that $l+m+n=0; l^2 +m^2-n^2=0$ then the angle between them is :

$\begin {array} {1 1} (a)\;\pi & \quad (b)\;\pi/3 \\ (c)\;\pi/4 & \quad (d)\;\pi/6 \end {array}$

Can you answer this question?

$(b) \pi/3$
answered Nov 7, 2013 by