The position vectors of the vertices A,B and C of a triangle are 2 i-3 j+3 k,2 i+2 j+3 k and - i+ j+3 k respectively. Let l denotes the length of the…
JEE Main 2024 — Mathematics Vectors & 3D Geometry
2024mcqeasy
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 :
Official previous-year question
Held on 27 Jan 2024 · Verified 6 Jul 2026.
Options
A
49
B
42
C
50
D
45
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Solution
Given: A(2,−3,3),B(2,2,3)andC(−1,1,3) are vertices of a △ABC.
AB=(2−2)2+(2+3)2+(3−3)2
⇒AB=5
⇒AC=(2+1)2+(−3−1)2+(3−3)2
⇒AC=9+16
⇒AC=5
Also, AD is the angle bisector of ∠BAC.
⇒ACAB=CDBD
⇒BD=CD
∴D is midpoint of BC
So, using mid-point formula,
⇒D≡(22−1,22+1,23+3)
⇒D≡(21,23,3)
⇒AD=l=(2−21)2+(−3−23)2+(3−3)2
⇒l=(23)2+(−29)2
⇒l=49+481
⇒l=245
⇒l2=245
⇒2l2=45
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