Let the position vectors of the vertices A,B and C of a triangle be 2 i+2 j+ k, i+2 j+2 k and 2 i+ j+2 k respectively. Let _1, _2 and _3 be the…
JEE Main 2024 — Mathematics Vectors & 3D Geometry
2024mcqmedium
Let the position vectors of the vertices A,B and C of a triangle be 2i^+2j^+k^,i^+2j^+2k^ and 2i^+j^+2k^ respectively. Let l1,l2 and l3 be the lengths of perpendiculars drawn from the ortho centre of the triangle on the sides AB,BC and CA respectively, then l12+l22+l32 equals :
Official previous-year question
Held on 27 Jan 2024 · Verified 6 Jul 2026.
Options
A
51
B
21
C
41
D
31
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Solution
Given: A(2,2,1),B(1,2,2)andC(2,1,2) are vertices of ΔABC.
⇒AB=(2−1)2+(2−2)2+(1−2)2=2
⇒BC=(1−2)2+(2−1)2+(2−2)2=2
⇒CA=(2−2)2+(2−1)2+(1−2)2=2
So, ΔABC is equilateral.
Therefore, orthocentre and centroid will be same.
⇒G≡(32+1+2,32+2+1,31+2+2)
⇒G≡(35,35,35)
Also, mid point of AB is D(23,2,23)
⇒l1=(23−35)2+(2−35)2+(23−35)2
⇒l1=361+91+361
⇒l1=61
Similarly, l2=l3=61
⇒(l1)2+(l2)2+(l3)2=61+61+61
⇒(l1)2+(l2)2+(l3)2=21
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