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JEE Mains · Maths · STD 12 - 10. vector algebra

Let \(\quad \overrightarrow{\mathrm{a}}=2 \hat{\mathrm{i}}+\alpha \hat{\mathrm{j}}+\hat{\mathrm{k}}, \quad \overrightarrow{\mathrm{b}}=-\hat{\mathrm{i}}+\hat{\mathrm{k}}, \quad \overrightarrow{\mathrm{c}}=\beta \hat{\mathrm{j}}-\hat{\mathrm{k}}\), where \(\alpha\) and \(\beta\) are integers and \(\alpha \beta=-6\). Let the values of the ordered pair \((\alpha, \beta)\) for which the area of the parallelogram of diagonals \(\vec{a}+\vec{b}\) and \(\vec{b}+\vec{c}\) is \(\frac{\sqrt{21}}{2}\), be \(\left(\alpha_1, \beta_1\right)\) and \(\left(\alpha_2, \beta_2\right)\). Then \(\alpha_1^2+\beta_1^2-\alpha_2 \beta_2\) is equal to

  1. A \(17\)
  2. B \(24\)
  3. C \(21\)
  4. D \(19\)
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Correct Answer

(D) \(19\)

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Detailed explanation

\( \text { Area of parallelogram } \left.=\frac{1}{2} \right\rvert\, \overrightarrow{\mathrm{d}}_1 \times \overrightarrow{\mathrm{d}}_2 \)…
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