Let P be the point (10,−2,−1) and Q be the foot of the perpendicular drawn from the point R(1,7,6) on the line passing through the points (2,−5,11) and (−6,7,−5). Then the length of the line segment PQ is equal to ____.
Answer: 13
Solution
The line through (2,−5,11) and (−6,7,−5) has direction (2,−3,4). The foot of the perpendicular from R(1,7,6) is Q(−2,1,3) (solving QR⋅(2,−3,4)=0). PQ=(−2−10,1−(−2),3−(−1))=(−12,3,4), so PQ=144+9+16=169=13.