A) 5
B) ? 5
C) 7
D) \[\frac{1}{7}\]
Correct Answer: A
Solution :
We know that as the vectors are perpendicular, therefore their dot product is zero or \[(a\mathbf{i}+6\mathbf{j}-\mathbf{k})\,.\,(7\mathbf{i}-3\mathbf{j}+17\mathbf{k})=0\] or \[7a-18-17=0\]or \[7a=35\] or \[a=5\].
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