If the vectors 3i+ ,j+k and 2i-j+8k are perpendicular, then is - Vidyadip

MCQ

If the vectors $3i+\lambda \,j+k$ and $2i-j+8k$ are perpendicular, then $\lambda $ is

A
$-14$
B
$7$
✓
$14$
D
$1/7$

✓

Answer

Correct option: C.

$14$

c
(c) Let $a = 3i + \lambda \,j + k$,$b = 2i - j + 8k$

$\because a \bot \,b$ $\therefore a\,.\,b = 0$

$(3i + \lambda \,j + k)\,.\,(2i - j + 8k) = 0$

$a,\,b,\,c$ $ \Rightarrow \lambda = 14.$

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