Medium MCQ +4 / -1 PYQ · JEE Mains 2021

If $\overrightarrow a$ and $\overrightarrow b$ are perpendicular, then
$$\overrightarrow a \times \left( {\overrightarrow a \times \left( {\overrightarrow a \times \left( {\overrightarrow a \times \overrightarrow b } \right)} \right)} \right)$$ is equal to :

  1. A ${1 \over 2}|\overrightarrow a {|^4}\overrightarrow b$
  2. B $\overrightarrow 0$
  3. C $\overrightarrow a \times \overrightarrow b$
  4. D $|\overrightarrow a {|^4}\overrightarrow b$ Correct answer

Solution

$\overrightarrow a \,.\,\overrightarrow b = 0$<br><br>$$\overrightarrow a \times (\overrightarrow a \times \overrightarrow b ) = (\overrightarrow a \,.\,\overrightarrow b )\overrightarrow a - (\overrightarrow a \,.\,\overrightarrow a )\overrightarrow b = - |\overrightarrow a {|^2}\overrightarrow b $$<br><br>Now, $$\overrightarrow a \times (\overrightarrow a \times ( - |\overrightarrow a {|^2}\overrightarrow b ))$$<br><br>$$ = - |\overrightarrow a {|^2}(\overrightarrow a \times (\overrightarrow a \times \overrightarrow b ))$$<br><br>$$ = - |\overrightarrow a {|^2}( - |\overrightarrow a {|^2}\overrightarrow b ) = |\overrightarrow a {|^4}\overrightarrow b $$

About this question

Subject: Mathematics · Chapter: Vector Algebra · Topic: Types of Vectors

This question is part of PrepWiser's free JEE Main question bank. 169 more solved questions on Vector Algebra are available — start with the harder ones if your accuracy is >70%.

Drill 25 more like these. Every day. Free.

PrepWiser turns these solved questions into a daily practice loop. Chapter-wise drills, full mocks, AI doubt chat. No auto-renew.

Start free →