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NDA 2017 Maths · Mathematics · Vector Algebra · easy

The angle between the vectors hat i+2hat j+2hat k and 2hat i-2hat j+hat k is

Single correct option

The angle between the vectors i^+2j^+2k^\hat i+2\hat j+2\hat k and 2i^−2j^+k^2\hat i-2\hat j+\hat k is
  1. A. 0∘0^\circ
  2. B. 45∘45^\circ
  3. C. 90∘90^\circ
  4. D. 60∘60^\circ
Show answer and solution

Answer: (C) 90∘90^\circ

The dot product is 2−4+2=02-4+2=0 while neither vector is zero, so they are perpendicular. Both vectors have magnitude 33, which makes the other angles tempting if the dot product is mis-added.
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Original question written in the NDA 2017 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake