<p>Help with a question - 3D geometry</p>
<p>Q. The angle between the two lines who’s D.C are given by 3l+m+5n = 0 and 6mn-2nl+5ml = 0</p>
<p>What does D.C. stand for? Are l, m, n coordinate axes? If so, the second equation is not a line.</p>
<p>DC - directional cosines.
l,m,n are directional cosines of x,y,z</p>
<p>Ah okay. Been a while since I’ve seen them.</p>
<p>bump bump bumty bump</p>