MathsJEE Main 28 Jan 2026, Shift 1·Q19·MCQ·Easy–moderate

Vectors · Magnitude and dot product

For three unit vectors

\vec a, \vec b, \vec c

satisfying

\lvert\vec a - \vec b\rvert^2 + \lvert\vec b - \vec c\rvert^2 + \lvert\vec c - \vec a\rvert^2 = 9

and

\lvert 2\vec a + k\vec b + k\vec c\rvert = 3

, the positive value of

k

is:

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