The distance of the point (1,−5,9) from the plane x−y+z=5 measured along the line x=y=z is:
(A)103✓ Correct
(B)310
(C)320
(D)310
Answer: (A)
Solution
First take the ordinary perpendicular distance from A(1,−5,9) to the plane x−y+z=5: 1+1+1∣1−(−5)+9−5∣=310. But the distance is measured along the line x=y=z, direction (1,1,1), tilted from the plane's normal (1,−1,1) by cosθ=331−1+1=31. The slant distance is the perpendicular distance divided by this cosine, 1/310/3=330=103.
JEE Main · 2016 · 03 Apr 2016 · Offline · Single correct option