Easy MCQ +4 / -1 PYQ · JEE Mains 2022

Let $\overrightarrow a = \widehat i + \widehat j - \widehat k$ and $\overrightarrow c = 2\widehat i - 3\widehat j + 2\widehat k$. Then the number of vectors $\overrightarrow b$ such that $\overrightarrow b \times \overrightarrow c = \overrightarrow a$ and $|\overrightarrow b | \in$ {1, 2, ........, 10} is :

  1. A 0 Correct answer
  2. B 1
  3. C 2
  4. D 3

Solution

<p>$\overrightarrow a = \widehat i + \widehat j - \widehat k$</p> <p>$\overrightarrow c = 2\widehat i - 3\widehat j + 2\widehat k$</p> <p>Now, $\overrightarrow b \times \overrightarrow c = \overrightarrow a$</p> <p>$$\overrightarrow c \,.\,(\overrightarrow b \times \overrightarrow c ) = \overrightarrow c \,.\,\overrightarrow a $$</p> <p>$\overrightarrow c \,.\,\overrightarrow a = 0$</p> <p>$$ \Rightarrow (\widehat i + \widehat j - \widehat k)(2\widehat i - 3\widehat j + 2\widehat k) = 0$$</p> <p>$= 2 - 3 - 2 = 0$</p> <p>$\Rightarrow - 3 = 0$ (Not possible)</p> <p>$\Rightarrow$ No possible value of $\overrightarrow b$ is possible.</p>

About this question

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

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