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