JEE Mains · Maths · STD 12 - 10. vector algebra
Between the following two statements : Statement \(-I\) : Let \(\overrightarrow{\mathrm{a}}=\hat{\mathrm{i}}+2 \hat{\mathrm{j}}-3 \hat{\mathrm{k}}\) and \(\vec{b}=2 \hat{i}+\hat{j}-\hat{k}\). Then the vector \(\vec{r}\) satisfying \(\overrightarrow{\mathrm{a}} \times \overrightarrow{\mathrm{r}}=\overrightarrow{\mathrm{a}} \times \overrightarrow{\mathrm{b}}\) and \(\overrightarrow{\mathrm{a}} \cdot \overrightarrow{\mathrm{r}}=0\) is of magnitude \(\sqrt{10}\). Statement \(-II\) : In a triangle \(A B C, \cos 2 A+\cos 2 B\) \(+\cos 2 \mathrm{C} \geq-\frac{3}{2}\)
- A Both Statement \(-I\) and Statement \(-II\) are incorrect
- B Statement \(-I\) is incorrect but Statement \(-II\) is correct
- C Both Statement \(-I\) and Statement \(-II\) are correct
- D Statement \(-I\) is correct but Statement \(-II\) is incorrect
Answer & Solution
Correct Answer
(B) Statement \(-I\) is incorrect but Statement \(-II\) is correct
Step-by-step Solution
Detailed explanation
\( \bar{a}=\hat{i}+2 \hat{j}-3 \hat{k} \) \( \bar{a}=2 \hat{i}+\hat{j}-\hat{k} \) \( \bar{a} \times \bar{r}=\bar{a} \times \bar{b} ; \bar{a} \cdot \bar{r}=0 \) \( \Rightarrow \bar{a} \times(\bar{r}-\bar{b})=\overline{0} \) \( \Rightarrow \bar{a}=\lambda(\bar{r}-\bar{b}) \)…
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