Let P and Q be the points on the line 8x+3=2y−4=2z+1 which are at a distance of 6 units from the point R(1,2,3). If the centroid of the triangle PQR is (α,β,γ), then α2+β2+γ2 is:
(A)26
(B)36
(C)18✓ Correct
(D)24
Answer: (C)
Solution
A general point on the line 8x+3=2y−4=2z+1=λ is (8λ−3,2λ+4,2λ−1).
Distance from R(1,2,3) equal to 6:
(8λ−4)2+(2λ+2)2+(2λ−4)2=36.
Expanding: 64λ2−64λ+16+4λ2+8λ+4+4λ2−16λ+16=36, i.e.
72λ2−72λ+36=36⟹72λ(λ−1)=0⟹λ=0 or 1.
λ=0 gives P(−3,4,−1); λ=1 gives Q(5,6,1).
Centroid of △PQR:
(3−3+5+1,34+6+2,3−1+1+3)=(1,4,1).
α2+β2+γ2=1+16+1=18.
JEE Main · 2024 · 01 Feb 2024 · Shift 2 · Single correct option