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

Let \(ABC\) be a triangle such that \(\overrightarrow{ BC }=\overrightarrow{ a }, \overrightarrow{ CA }=\overrightarrow{ b }\), \(\overrightarrow{ AB }=\overrightarrow{ c },|\overrightarrow{ a }|=6 \sqrt{2}, \quad|\overrightarrow{ b }|=2 \sqrt{3}\) and \(\overrightarrow{ b } \cdot \overrightarrow{ c }=12\) Consider the statements. \(( S 1):|(\overrightarrow{ a } \times \overrightarrow{ b })+(\overrightarrow{ c } \times \overrightarrow{ b })|-|\overrightarrow{ c }|=6(2 \sqrt{2}-1)\) \(( S 2): \angle ABC =\cos ^{-1}\left(\sqrt{\frac{2}{3}}\right)\). Then

  1. A both \(( S 1)\) and \(( S 2)\) are true 
  2. B only \((S1)\) is true
  3. C only \((S 2)\) is true
  4. D both \(( S 1)\) and \(( S 2)\) are false
Verified Solution

Answer & Solution

Correct Answer

(C) only \((S 2)\) is true

Step-by-step Solution

Detailed explanation

\(\overrightarrow{ a }+\overrightarrow{ b }+\overrightarrow{ c }=0\) \(\overrightarrow{ b }+\overrightarrow{ c }=-\overrightarrow{ a }\) \(|\overrightarrow{ b }|^{2}+|\overrightarrow{ c }|^{2}+2 \overrightarrow{ b } \cdot \overrightarrow{ c }=|\overrightarrow{ a }|^{2}\)…