Let overrightarrow{OA} = hat{i} - 3hat{j} + h | vedclass

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(D) The position vector of point $P$ which divides $AB$ in the ratio $2:1$ is given by the section formula:$\vec{r} = \frac{2(\overrightarrow{OB}) + 1

Vedclass · Accepted Answer

$3$

Vedclass · Answer

(D) The position vector of point $P$ which divides $AB$ in the ratio $2:1$ is given by the section formula:$\vec{r} = \frac{2(\overrightarrow{OB}) + 1(\overrightarrow{OA})}{2+1} = \frac{2(\hat{i} + 3\hat{j} - 2\hat{k}) + 1(\hat{i} - 3\hat{j} + \hat{k})}{3}$$= \frac{2\hat{i} + 6\hat{j} - 4\hat{k} + \hat{i} - 3\hat{j} + \hat{k}}{3} = \frac{3\hat{i} + 3\hat{j} - 3\hat{k}}{3} = \hat{i} + \hat{j} - \hat{k}$Now, the vector $\overrightarrow{PC} = \overrightarrow{OC} - \vec{r} = (4\hat{i} + 3\hat{j} + 5\hat{k}) - (\hat{i} + \hat{j} - \hat{k}) = 3\hat{i} + 2\hat{j} + 6\hat{k}$The magnitude of $\overrightarrow{PC}$ is $|\overrightarrow{PC}| = \sqrt{3^2 + 2^2 + 6^2} = \sqrt{9 + 4 + 36} = \sqrt{49} = 7$The direction cosines $(l, m, n)$ of $\overrightarrow{PC}$ are given by $\frac{\vec{v}}{|\vec{v}|}$:$l = \frac{3}{7}, m = \frac{2}{7}, n = \frac{6}{7}$Therefore, $l + 3m + 2n = \frac{3}{7} + 3(\frac{2}{7}) + 2(\frac{6}{7}) = \frac{3 + 6 + 12}{7} = \frac{21}{7} = 3$

Similar Questions

If $\vec{a}=\hat{i}+\hat{j}+2 \hat{k}$ and $\vec{b}=2 \hat{i}+\hat{j}+2 \hat{k},$ find the unit vector in the direction of
$(i)$ $6 \vec{b}$
(ii) $2 \vec{a}-\vec{b}$

If $\vec{a}, \vec{b}, \vec{c}$ are the position vectors of points $A, B, C$ respectively,and $D$ is the midpoint of $BC$,then $\vec{AD} = \dots$

If $\vec{a}, \vec{b}, \vec{c}$ are $3$ vectors such that $|\vec{a}|=5, |\vec{b}|=8, |\vec{c}|=11$ and $\vec{a}+\vec{b}+\vec{c}=\overrightarrow{0}$,then the angle between the vectors $\vec{a}$ and $\vec{b}$ is

If $\vec{a}=\hat{i}+\hat{j}+\hat{k}, \vec{b}=2 \hat{i}-\hat{j}+3 \hat{k}$ and $\vec{c}=\hat{i}-2 \hat{j}+\hat{k},$ find a unit vector parallel to the vector $2 \vec{a}-\vec{b}+3 \vec{c}.$

Show that each of the given three vectors is a unit vector:
$\frac{1}{7}(2 \hat{i}+3 \hat{j}+6 \hat{k}), \frac{1}{7}(3 \hat{i}-6 \hat{j}+2 \hat{k}), \frac{1}{7}(6 \hat{i}+2 \hat{j}-3 \hat{k})$
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