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Question: Answered & Verified by Expert
The position vectors of the vertices A, B and C of a triangle are 2i^-3j^+3k^, 2i^+2j^+3k^ and -i^+j^+3k^ respectively. Let l denotes the length of the angle bisector AD of BAC where D is on the line segment BC, then 2l2 equals :
MathematicsThree Dimensional GeometryJEE MainJEE Main 2024 (27 Jan Shift 2)
Options:
  • A 49
  • B 42
  • C 50
  • D 45
Solution:
1122 Upvotes Verified Answer
The correct answer is: 45

Given: A2,-3,3, B2,2,3 and C-1,1,3 are vertices of a ABC.

AB=2-22+2+32+3-32

AB=5

AC=2+12+-3-12+3-32

AC=9+16

AC=5

Also, AD is the angle bisector of BAC.

ABAC=BDCD

BD=CD

 D is midpoint of BC

So, using mid-point formula,

D2-12,2+12,3+32

D12,32,3

AD=l=2-122+-3-322+(3-3)2

l=322+-922

l=94+814

l=452

l2=452

2l2=45

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