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Provide solution for RD Sharma maths class 12 chapter 22 Algebra of Vectors exercise Multiple choice question 14

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Answer: Form as isosceles triangle.

Hint: ABC for which triangle

Given: The position vector of pointsA, B and Care 2 \vec{i}+\vec{j}-\vec{k}, 3 \vec{i}-2 \vec{j}+\vec{k}, i+4 j-3 k

Solution:

        \begin{aligned} &\overrightarrow{O A}=2 \hat{i}+\hat{j}-\hat{k}, \\\\ &\overrightarrow{O B}=3 \hat{i}-2 \hat{j}+\hat{k}, \\\\ &\overrightarrow{O C}=\hat{i}+4 \hat{j}-3 \hat{k} \end{aligned}

        \begin{aligned} &\overrightarrow{A B}=\overrightarrow{O B}-\overrightarrow{O A} \\\\ &=(3-2) \hat{i}+(-2-1) \hat{j}+(1+1) \hat{k} \\\\ &=\hat{i}-3 \hat{j}+2 \hat{k} \end{aligned}

        \begin{aligned} &|\overrightarrow{A B}|=\sqrt{1^{2}+3^{2}+2^{2}}=\sqrt{1+9+4}=\sqrt{14} \\\\ &\overrightarrow{B C}=\overrightarrow{O C}-\overrightarrow{O B} \\\\ &=(1-3) \hat{i}+(4+2) \hat{j}+(-3-1) \hat{k} \\\\ &=-2 \hat{i}+6 \hat{j}-4 \hat{k} \end{aligned}

        \begin{aligned} &|\overrightarrow{B C}|=\sqrt{(2)^{2}+6^{2}+(-4)^{2}}=\sqrt{4+36+16}=\sqrt{56}=2 \sqrt{14} \\\\ &\overrightarrow{C A}=\overrightarrow{O A}-\overrightarrow{O C} \\\\ &=(2-1) \hat{i}+(1-4) \hat{j}+(-1+3) \hat{k} \end{aligned}

        \begin{aligned} &=\hat{i}-3 \hat{j}+2 \hat{k} \\\\ &|\overrightarrow{C A}|=\sqrt{1^{2}+3^{2}+2^{2}}=\sqrt{1+9+4}=\sqrt{14} \end{aligned}

       

        Hence \overrightarrow{A B}\; \& \; \overrightarrow{C A}=\sqrt{14}

        It forms isosceles triangle.

 

 

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