Let P be a point in the plane of the vectors overrightarrowA B=3 i+ j- k and overrightarrowA C= i- j+3 k such that P is equidistant from the lines AB…
JEE Main 2026 — Mathematics Vectors & 3D Geometry
2026mcqhard
Let P be a point in the plane of the vectors AB=3i^+j^−k^ and AC=i^−j^+3k^ such that P is equidistant from the lines AB and AC. If ∣AP∣=25, then the area of the triangle ABP is:
Official previous-year question
Held on 28 Jan 2026 · Verified 6 Jul 2026.
Options
A
2
B
430
C
23
D
426
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Solution
Since P is equidistant from lines AB and AC through point A, it lies along the angle bisector direction. The unit vectors are u^AB=113i+j−k and u^AC=11i−j+3k.
The bisector direction is proportional to 2i+k, so AP=λ(2i+k).
From ∣AP∣=25: ∣λ∣5=25, giving λ=21.
Thus AP=i+21k.
Area of triangle ABP = 21∣AB×AP∣.
Computing: AB×AP=21i−25j−k.
∣AB×AP∣=41+425+1=430=230.
Area = 430.
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