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Explain solution RD Sharma class 12 Chapter 22 Algebra of Vectors Exercise 22.6 question 10 subquestion (ii)

Answers (1)

Answer:

-3 \hat{\imath}+\hat{k}

Hint:

Use position vector formula.

Given:

P(\hat{\imath}+2 \hat{\jmath}+\hat{k}) \text { and } Q(-\hat{\imath}+\hat{\jmath}+\hat{k})  i the ratio 2:1

Solution:

Position vector of P and Q are given as:

\begin{aligned} &O \vec{P}=(\hat{\imath}+2 \hat{\jmath}+\hat{k}) \text { and } O \vec{Q}=(-\hat{\imath}+\hat{\jmath}+\hat{k}) \\\\ &\frac{m}{n}=\frac{2}{1} \end{aligned}

 

The position vector of point R which divides the line joining two points P and Q externally in the ratio 2 : 1 is given by:

 

A vector divides an line Internally as in m:n  Externally  =\frac{m \vec{Q}-n \vec{p}}{m-n}

\begin{aligned} &O \vec{R}=\frac{(\hat{\imath}+2 \hat{\jmath}+\hat{k})-2(-\hat{\imath}+\hat{\jmath}+\hat{k})}{1-2}=\frac{3 \hat{\imath}-\hat{k}}{-1} \\\\ &O \vec{R}=-3 \hat{\imath}+\hat{k} \end{aligned}

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