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TS EAMCET · Maths · Vector Algebra

Let \(\overrightarrow{\mathbf{a}}=a_1 \hat{\mathbf{i}}+a_2 \hat{\mathbf{j}}+a_3 \hat{\mathbf{k}}\) Assertion (A) : The identity \(|\overrightarrow{\mathbf{a}} \times \hat{\mathbf{i}}|^2+|\overrightarrow{\mathbf{a}} \times \hat{\mathbf{j}}|^2+|\overrightarrow{\mathbf{a}} \times \hat{\mathbf{k}}|^2=2|\overrightarrow{\mathbf{a}}|^2\) holds for \(\vec{a}\). Reason (R) : \(\overrightarrow{\mathbf{a}} \times \hat{\mathbf{i}}=a_3 \hat{\mathbf{j}}-a_2 \hat{\mathbf{k}}\), \(\overrightarrow{\mathbf{a}} \times \hat{\mathbf{j}}=a_1 \hat{\mathbf{k}}-a_3 \hat{\mathbf{i}}, \overrightarrow{\mathbf{a}} \times \hat{\mathbf{k}}=a_2 \hat{\mathbf{i}}-a_1 \hat{\mathbf{j}}\) Which of the following is correct?

  1. A Both \((\mathrm{A})\) and \((\mathrm{R})\) are true and \((\mathrm{R})\) is the correct reason for (A)
  2. B Both \((A)\) and \((R)\) are true but \((R)\) is not the correct reason for (A)
  3. C (A) is true, (R) is false
  4. D (A) is false, (R) is true
Verified Solution

Answer & Solution

Correct Answer

(A) Both \((\mathrm{A})\) and \((\mathrm{R})\) are true and \((\mathrm{R})\) is the correct reason for (A)

Step-by-step Solution

Detailed explanation

Given, \(\overrightarrow{\mathbf{a}}=a_1 \hat{\mathbf{i}}+a_2 \hat{\mathbf{j}}+a_3 \hat{\mathbf{k}}\) Now, \(|\overrightarrow{\mathbf{a}} \times \hat{\mathbf{i}}|^2=(\overrightarrow{\mathbf{a}} \times \hat{\mathbf{i}}) \cdot(\overrightarrow{\mathbf{a}} \times \hat{\mathbf{i}})\)…