Since equation of line joining points B(4,7,1) and C(3,5,3) is ‌
x−4
4−3
=‌
y−7
7−5
=‌
z−1
1−3
⇒‌‌‌
x−4
1
=‌
y−7
2
=‌
3−1
−2
=λ  (let)....(i) Now the general point over the above line (i) is P(λ+4,2λ+7,1−2λ) Let point P is the foot of perpendicular of point A(1,0,3) over the line (i), so AP ⟂ line