A1,2,3,B4,5,7,C−4,3,−6,D2,k2,2 are four points. If the lines AB→ and CD→ are parallel, then k=

If two lines are parallel, then their direction ratios are in proportional The direction ration of line joining Ax1,y1,z1 and Bx2,y2,z2 is x2−x1,y2−y1,z2−z1The direction ration of line joining A1,2,3 and B4,5,7 is3,3,4The direction ration of line joining C−4,3,−6 and D2,k2,2 is6,k2−3,8Since the lines are parallel, their direction ratios are proportional. It implies that63=k2−33=84Therefore, k2−3=6⇒k2=9⇒k=±3