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

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Answer: \frac{\sqrt{35}}{2}

Hint: The length of median by median formula

Given: The vector 2 \hat{j}+\hat{k} \& 3 \hat{i}-\hat{j}+4 \hat{k}  represent two side \mathrm{AB}\; \&\; \mathrm{AC} \text { of } \Delta A B C. Find length of median,

Solution:

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

                \begin{aligned} &\overrightarrow{B D}=\frac{1}{2} B C \Rightarrow \frac{3}{2} \hat{i}-\frac{3}{2} \hat{j}+\frac{3}{2} \hat{k} \\\\ &\overrightarrow{A D}=A B+B D \\\\ &=(2 \hat{j}+\hat{k})+\left(\frac{3}{2} \hat{i}-\frac{3}{2} \hat{j}+\frac{3}{2} \hat{k}\right) \end{aligned}

                \begin{gathered} \overrightarrow{A D}=\frac{3}{2} \hat{\imath}+\frac{1}{2} \hat{\jmath}+\frac{5}{2} \hat{k} \\\\ |A D|=\sqrt{\left(\frac{3}{2}\right)^{2}+\left(\frac{1}{2}\right)^{2}+\left(\frac{5}{2}\right)^{2}} \end{gathered}

                =\sqrt{\frac{9}{4}+\frac{1}{4}+\frac{25}{4}}=\sqrt{\frac{35}{4}}=\frac{\sqrt{35}}{2}

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