Equation of line through points (1,-2,3) and (1,1,0) is
x−1
0
=
y−1
−3
=
z−0
3−0
(=λ say ) ∴M(1,−λ+1,λ) Direction ratios of PM=[−3,−λ−1,λ−3] ∵PM⊥AB ∴(−3).0+(−1−λ)(−1)+(λ−3).1=0 ∴λ=1 ∴ Foot of perpendicular =(1,0,1) This point satisfy the plane 2x+y−z=1