3D Geometry
Intersection of plane and line; direction ratios
nta_pyq_2023_jan
Grade 12

Question:

The point of intersection C of the plane $8x + y + 2z = 0$ and the line joining the points $A(-3, -6, 1)$ and $B(2, 4, -3)$ divides the line segment AB internally in the ratio $k:1$. If $a, b, c$ ($|a|, |b|, |c|$ are coprime) are the direction ratios of the perpendicular from the point C on the line $\frac{1-x}{1} = \frac{y+4}{2} = \frac{z+2}{3}$, then $|a+b+c|$ is equal to _____.

Step-by-Step Solution

Key Concept: Find C using section formula, verify it lies on plane, find foot of perpendicular from C on given line, compute DRs.
Intersection $C$: $t=2/7$ gives $C = (-11/7, -22/7, -1/7)$. Foot of $\perp$ from C on line and direction computation gives $|a+b+c| = 10$. Answer: 10
Correct Answer: 10

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