DR's of OP=<1−0.2−0.3−0>=<1,2,3> since OP is perpendicular to the plane, therefore OP is normal to the plane. The equation of the plane passing through (1,2,3) and having d′r<1,2,3> of its normal is 1(x−1)+2(y−2)+3(z−3)=0 x+2y+3z−14=0 Thus the (7,2,1) lies on the given plane