Let a line L passing through the point (1,1,1) be perpendicular to both the vectors 2i^+2j^+k^ and i^+2j^+k^. If P(a,b,c) is the foot of perpendicular from the origin on the line L, then the value of 34(a+b+c) is :
(A)50
(B)80
(C)100✓ Correct
(D)120
Answer: (C)
Solution
The direction of L is perpendicular to both given vectors, so d=(2i^+2j^+k^)×(i^+2j^+2k^)=2i^−3j^+2k^, with ∣d∣2=17. Writing L:(1,1,1)+λ(2,−3,2), a general point is (1+2λ,1−3λ,1+2λ). The foot of the perpendicular from the origin satisfies (1+2λ,1−3λ,1+2λ)⋅(2,−3,2)=0, i.e. 2(1+2λ)−3(1−3λ)+2(1+2λ)=1+17λ=0, so λ=−171. Then P=(1715,1720,1715) and a+b+c=1750, giving 34(a+b+c)=34⋅1750=100.
JEE Main · 2026 · 02 Apr 2026 · Shift 1 · Single correct option