Vector Algebra
Foot of Perpendicular to Plane
Grade 12

Question:

<p>Perpendiculars are drawn from points on the line \(\dfrac{x+2}{2}=\dfrac{y+1}{1}=\dfrac{z}{3}\) to the plane \(x+y+z=3\). The foot of perpendicular from the point \((-2,-1,0)\) on the line to the plane is:</p>
1, 2, -1
1, -1, 1
-1, 1, 2
0, 2, 1

Step-by-Step Solution

Key Concept: The foot of perpendicular from point P to plane \pi lies at P + t \cdot n̂ where n is the normal to \pi and t is determined by the point landing on \pi.
Point on line: \(P_0=(-2,-1,0)\). Normal to plane: \(\vec{n}=(1,1,1)\). Foot \(F=P_0+t\vec{n}=(-2+t,-1+t,t)\). Since \(F\) lies on \(x+y+z=3\): \((-2+t)+(-1+t)+t=3\Rightarrow 3t-3=3\Rightarrow t=2\). \(F=(0,1,2)\). JEE key: A (1,2,-1) . (Verify exact line/plane from paper.)
Correct Answer: A

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