Three Dimensional Geometry

Find the vector equation of the line passing through $(1,2,3)$ and parallel to the planes $\overrightarrow{\mathrm{r}} \cdot(\hat{\mathrm{i}}-\hat{\mathrm{j}}+2 \hat{\mathrm{k}})=5$ and $\overrightarrow{\mathrm{r}} \cdot(3 \hat{\mathrm{i}}+\hat{\mathrm{j}}+\hat{\mathrm{k}})=6$

Solution: The vector eq. of a line passing through a point with position vector $\vec{a}$ and parallel to a vector $\vec{b}$ is $\vec{r}=\vec{a}+\lambda \vec{b}$ It is given that the line passes...

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Find the distance of the point $(-1,-5,-10)$ from the point of intersection of the line $\overrightarrow{\mathrm{r}}=(2 \hat{\mathrm{i}}-\hat{\mathrm{j}}+2 \hat{\mathrm{k}})+\lambda(3 \hat{\mathrm{i}}+4 \hat{\mathrm{j}}+2 \hat{\mathrm{k}})$ and the plane $\overrightarrow{\mathrm{r}} \cdot(\hat{\mathrm{i}}-\hat{\mathrm{j}}+\hat{\mathrm{k}})=5$

Solution: It is given that, The eq. of line is $\overrightarrow{\mathrm{r}}=(2 \hat{\mathrm{i}}-\hat{\mathrm{j}}+2 \hat{\mathrm{k}})+\lambda(3 \hat{\mathrm{i}}+4 \hat{\mathrm{j}}+2 \hat{\mathrm{k}})...

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Find the equation of the plane which contains the line of intersection of the planes $\vec{r} \cdot(\hat{1}+2 \hat{j}+3 \hat{k})-4=0$ and $\vec{r} \cdot(2 \hat{i}+\hat{j}-\hat{k})+5=0$ And which is perpendicular to the plane $\overrightarrow{\mathrm{r}} \cdot(5 \hat{\mathrm{i}}+3 \hat{\mathrm{j}}-6 \hat{\mathrm{k}})+8=0$

Solution: It is known that, The eq. of any plane through the line of intersection of the planes $\overrightarrow{\mathrm{r}} \cdot \overrightarrow{\mathrm{n}_{1}}=\mathrm{d}_{1}$ and...

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Find the equation of the plane passing through the line of intersection of the planes $\vec{r} \cdot(\hat{i}+\hat{j}+\hat{k})=1$ and $\vec{r} \cdot(2 \hat{i}+3 \hat{j}-\hat{k})+4=0$ and parallel to $x$-axis.

Solution: It is known to us that, The eq. of any plane through the line of intersection of the planes $\vec{r} \cdot \overrightarrow{n_{1}}=d_{1}$ and $\vec{r} \cdot \overrightarrow{n_{2}}=d_{2}$ is...

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Find the shortest distance between lines $\vec{r}=(6 \hat{i}+2 \hat{j}+2 \hat{k})+\lambda(1 \hat{i}-2 \hat{j}+\hat{2}) \text { and } \overrightarrow{1}=(-4 \hat{i}-\hat{k})+\mu(3 \hat{i}-2 \hat{j}-2 \hat{k})$

Solution: It is known to us that the shortest distance between lines with vector equations $\vec{r}=\overrightarrow{a_{1}}+\lambda \overrightarrow{b_{1}}$ and $\vec{r}=\overrightarrow{a_{2}}+\lambda...

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If $\mathrm{l}_{1}, \mathrm{~m}_{1}, \mathrm{n}_{1}$ and $\mathrm{l}_{2}, \mathrm{~m}_{2}, \mathrm{n}_{2}$ are the direction cosines of two mutually perpendicular lines, show that the direction cosines of the line perpendicular to both of these are $\left(\mathrm{m}_{1} \mathrm{n}_{2}-\mathrm{m}_{2} \mathrm{n}_{1}\right),\left(\mathrm{n}_{1} \mathrm{l}_{2}-\mathrm{n}_{2} \mathrm{l}_{1}\right),\left(\mathrm{l}_{1} \mathrm{~m}_{2}-\mathrm{l}_{2} \mathrm{~m}_{1}\right)$

Solution: Let's consider $l, m, n$ be the direction cosines of the line perpendicular to each of the given lines. Therefore, $ll_{1}+m m_{1}+n n_{1}=0 \ldots(1)$ And...

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In the following cases, determine whether the given planes are parallel or perpendicular, and in case they are neither, find the angles between them.
(a) 2x – 2y + 4z + 5 = 0 and 3x – 3y + 6z – 1 = 0
(b) 2x – 2y + 4z + 5 = 0 and 3x – 3y + 6z – 1 = 0

Solution: (a) $2 x-2 y+4 z+5=0$ and $3 x-3 y+6 z-1=0$ It is given that The eq. of the given planes are $2 x-2 y+4 z+5=0$ and $x-2 y+5=0$ It is known to us that, two planes are $\perp$ if the...

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In the following cases, determine whether the given planes are parallel or perpendicular, and in case they are neither, find the angles between them.
(a) 7x + 5y + 6z + 30 = 0 and 3x – y – 10z + 4 = 0
(b) 2x + y + 3z – 2 = 0 and x – 2y + 5 = 0

Solution: (a) $7 x+5 y+6 z+30=0$ and $3 x-y-10 z+4=0$ It is given that The eq. of the given planes are $7 x+5 y+6 z+30=0$ and $3 x-y-10 z+4=0$ Two planes are $\perp$ if the direction ratio of the...

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Find the vector and Cartesian equations of the planes
(a) that passes through the point $(1,0,-2)$ and the normal to the plane is $\hat{i}+\hat{j}-\hat{k}$
(b) that passes through the point $(1,4,6)$ and the normal vector to the plane is $\hat{i}-2 \hat{j}+\hat{k}$

Solution: (a) That passes through the point $(1,0,-2)$ and the normal to the plane is $\hat{\mathrm{i}}+\hat{\mathrm{j}}-\hat{\mathrm{k}}$ Let's say that the position vector of the point $(1,0,-2)$...

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Find the shortest distance between the lines whose vector equations are $\begin{array}{l} \vec{r}=(1-t) \hat{i}+(t-2) \hat{j}+(3-2 t) \hat{k} \text { and } \\ \vec{r}=(s+1) \hat{i}+(2 s-1) \hat{j}-(2 s+1) \hat{k} \end{array}$

Solution: Consider the given equations $\begin{array}{l} \Rightarrow \vec{r}=(1-t) \hat{i}+(t-2) \hat{j}+(3-2 t) \hat{k} \\ \vec{r}=\hat{i}-t \hat{i}+t \hat{j}-2 \hat{j}+3 \hat{k}-2 t \hat{k} \\...

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Find the shortest distance between the lines whose vector equations are $\vec{r}=(\hat{i}+2 \hat{j}+3 \hat{k})+\lambda(\hat{i}-3 \hat{j}+2 \hat{k})$ and $\vec{r}=4 \hat{i}+5 \hat{j}-6 \hat{k}+\mu(2 \hat{i}+3 \hat{j}+\hat{k})$

Solution: It is known to us that shortest distance between two lines $\vec{r}=\overrightarrow{a_{1}}+\lambda \overrightarrow{b_{1}}$ and $\vec{r}=\overrightarrow{a_{2}}+\mu \overrightarrow{b_{2}}$...

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Find the angle between the following pairs of lines:
(i) $\vec{r}=2 \hat{i}-5 \hat{j}+\hat{k}+\lambda(3 \hat{i}+2 \hat{j}+6 \hat{k})$ and $\overrightarrow{\mathrm{r}}=7 \hat{\mathrm{i}}-6 \hat{\mathrm{k}}+\mu(\hat{\mathrm{i}}+2 \hat{\mathrm{j}}+2 \hat{\mathrm{k}})$
(ii) $\vec{r}=3 \hat{i}+\hat{j}-2 \hat{k}+\lambda(\hat{i}-\hat{j}-2 \hat{k})$ and $\overrightarrow{\mathrm{r}}=2 \hat{\mathrm{i}}-\overrightarrow{\mathrm{j}}-56 \hat{\mathrm{k}}+\mu(3 \hat{\mathrm{i}}-5 \hat{\mathrm{j}}-4 \hat{\mathrm{k}})$

Solution: Let's consider $\theta$ be the angle between the given lines. If $\theta$ is the acute angle between $\vec{r}=\overrightarrow{a_{1}}+\lambda \overrightarrow{b_{1}}$ and...

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Find the equation of the line in vector and in Cartesian form that passes through the point with position vector $2 \hat{\mathrm{i}}-\hat{\mathrm{j}}+4 \hat{\mathrm{k}}$ and $\hat{\mathrm{i}}+2 \hat{\mathrm{j}}-\hat{\mathrm{k}}$. is in the direction

Solution: Given: Vector equation of a line that passes through a given point whose position vector is $\vec{a}$ and parallel to a given vector $\vec{b}$ is $\vec{r}=\vec{a}+\lambda \vec{b}$ Let,...

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If A and B be the points \[\left( \mathbf{3},\text{ }\mathbf{4},\text{ }\mathbf{5} \right)\]and \[\left( \mathbf{1},\text{ }\mathbf{3},\text{ }\mathbf{7} \right)\], respectively, find the equation of the set of points P such that \[\mathbf{P}{{\mathbf{A}}^{\mathbf{2}}}~+\text{ }\mathbf{P}{{\mathbf{B}}^{\mathbf{2}}}~=\text{ }{{\mathbf{k}}^{\mathbf{2}}}\], where k is a constant.

Given: The points A \[\left( \mathbf{3},\text{ }\mathbf{4},\text{ }\mathbf{5} \right)\]and B \[\left( \mathbf{1},\text{ }\mathbf{3},\text{ }\mathbf{7} \right)\]...

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A point R with x-coordinate \[4\] lies on the line segment joining the points P \[\left( \mathbf{2},\text{ }\mathbf{3},\text{ }\mathbf{4} \right)\]and Q \[\left( \mathbf{8},\text{ }\mathbf{0},\text{ }\mathbf{10} \right)\].Find the coordinates of the point R. [Hint Suppose R divides PQ in the ratio \[\mathbf{k}:\text{ }\mathbf{1}\]. The coordinates of the point R are given by

Solution: Given: The coordinates of the points P \[\left( \mathbf{2},\text{ }\mathbf{3},\text{ }\mathbf{4} \right)\] and Q \[\left( \mathbf{8},\text{ }\mathbf{0},\text{ }\mathbf{10} \right)\]. Let...

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. If the origin is the centroid of the triangle PQR with vertices P\[(\mathbf{2a},\text{ }\mathbf{2},\text{ }\mathbf{6})\], Q \[\left( \text{ }\mathbf{4},\text{ }\mathbf{3b},\text{ }\mathbf{10} \right)\]and R\[\left( \mathbf{8},\text{ }\mathbf{14},\text{ }\mathbf{2c} \right)\],then find the values of a, b and c.

Given: The vertices of the triangle are P (2a, 2, 6), Q (-4, 3b, -10) and R (8, 14, 2c). We know that the coordinates of the centroid of the triangle, whose vertices are \[({{x}_{1}},\text{...

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Find the lengths of the medians of the triangle with vertices A \[\left( \mathbf{0},\text{ }\mathbf{0},\text{ }\mathbf{6} \right)\],B \[\left( \mathbf{0},\text{ }\mathbf{4},\text{ }\mathbf{0} \right)\]and \[\left( 6,\text{ }0,\text{ }0 \right)\].

According to the question: The vertices of the triangle are A \[\left( \mathbf{0},\text{ }\mathbf{0},\text{ }\mathbf{6} \right)\],B \[\left( \mathbf{0},\text{ }\mathbf{4},\text{ }\mathbf{0}...

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Three vertices of a parallelogram ABCD are A\[\left( \mathbf{3},\text{ }\text{ }\mathbf{1},\text{ }\mathbf{2} \right)\], B \[\left( \mathbf{1},\text{ }\mathbf{2},\text{ }\text{ }\mathbf{4} \right)\]and C \[\left( \text{ }\mathbf{1},\text{ }\mathbf{1},\text{ }\mathbf{2} \right)\].Find the coordinates of the fourth vertex.

According to the question: ABCD is a parallelogram, with vertices A\[\left( \mathbf{3},\text{ }\text{ }\mathbf{1},\text{ }\mathbf{2} \right)\], B \[\left( \mathbf{1},\text{ }\mathbf{2},\text{...

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Find the coordinates of the points which trisect the line segment joining the points P \[\left( \mathbf{4},\text{ }\mathbf{2},\text{ }\text{ }\mathbf{6} \right)\]and Q \[\left( \mathbf{10},\text{ }\mathbf{16},\text{ }\mathbf{6} \right)\].

Consider A \[({{x}_{1}},\text{ }{{y}_{1}},\text{ }{{z}_{1}})\]and B \[({{x}_{2}},\text{ }{{y}_{2}},\text{ }{{z}_{2}})\]trisect the line segment joining the points P \[\left( \mathbf{4},\text{...

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Using section formula, show that the points A \[\left( \mathbf{2},\text{ }\mathbf{3},\text{ }\mathbf{4} \right)\], B \[\left( \mathbf{1},\text{ }\mathbf{2},\text{ }\mathbf{1} \right)\]and C \[\left( \mathbf{0},\text{ }\mathbf{1}/\mathbf{3},\text{ }\mathbf{2} \right)~\]are collinear.

Consider the point P divides AB in the ratio \[k:\text{ }1\]. By using section formula, So we have, Now, we check if for some value of k, the point coincides with the point C. Put \[\left( -k+2...

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Find the ratio in which the YZ-plane divides the line segment formed by joining the points \[\left( -\mathbf{2},\text{ }\mathbf{4},\text{ }\mathbf{7} \right)\]and \[\left( \mathbf{3},-\text{ }\mathbf{5},\text{ }\mathbf{8} \right)\].

Solution: Let the line segment formed by joining the points A \[\left(-\mathbf{2},\text{ }\mathbf{4},\text{ }\mathbf{7} \right)\]and B \[\left( \mathbf{3},-\text{ }\mathbf{5},\text{ }\mathbf{8}...

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Given that A \[\left( \mathbf{3},\text{ }\mathbf{2},\text{ }\text{ }\mathbf{4} \right)\], B \[\left( \mathbf{5},\text{ }\mathbf{4},\text{ }\text{ }\mathbf{6} \right)\]and C \[\left( \mathbf{9},\text{ }\mathbf{8},\text{ }\mathbf{10} \right)\]are collinear. Find the ratio in which B divides AC.

Solution: Let us consider B divides AC  in the ratio \[k:\text{ }1\]. By using section formula, So, we have \[9k\text{ }+\text{ }3\text{ }=\text{ }5\text{ }\left( k+1 \right)\] \[9k\text{ }+\text{...

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Find the coordinates of the point which divides the line segment joining the points \[\left( \text{ }\mathbf{2},\text{ }\mathbf{3},\text{ }\mathbf{5} \right)\]and \[\left( \mathbf{1},\text{ }\text{ }\mathbf{4},\text{ }\mathbf{6} \right)\]in the ratio (i) \[\mathbf{2}:\text{ }\mathbf{3}\]internally, (ii) \[\mathbf{2}:\text{ }\mathbf{3}\]externally.

Solution: Let the line segment joining the points A \[\left( \text{ }\mathbf{2},\text{ }\mathbf{3},\text{ }\mathbf{5} \right)\]and B \[\left( \mathbf{1},\text{ }\text{ }\mathbf{4},\text{ }\mathbf{6}...

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Find the equation of the set of points A, the sum of whose distances from p \[\left( \mathbf{4},\text{ }\mathbf{0},\text{ }\mathbf{0} \right)\] and q \[\left( \text{ }\mathbf{4},\text{ }\mathbf{0},\text{ }\mathbf{0} \right)\]is equal to 10.

Let p \[\left( \mathbf{4},\text{ }\mathbf{0},\text{ }\mathbf{0} \right)\]& q \[\left( \text{ }\mathbf{4},\text{ }\mathbf{0},\text{ }\mathbf{0} \right)\] Let the coordinates of point A be (x, y,...

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Verify the following: \[\left( 1,\text{ }2,\text{ }1 \right)\] , \[\left( 1,\text{ }2,\text{ }5 \right)\] , \[\left( 4,\text{ }7,\text{ }8 \right)\] and \[\left( 2,\text{ }3,\text{ }4 \right)\]are the vertices of a parallelogram.

Let the points be: p\[\left( 1,\text{ }2,\text{ }1 \right)\], q\[\left( 1,\text{ }2,\text{ }5 \right)\],r\[\left( 4,\text{ }7,\text{ }8 \right)\] & s\[\left( 2,\text{ }3,\text{ }4 \right)\] pqrs...

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Show that the points \[\left( \mathbf{2},\text{ }\mathbf{3},\text{ }\mathbf{5} \right)\], \[\left( \mathbf{1},\text{ }\mathbf{2},\text{ }\mathbf{3} \right)\]and \[\left( \mathbf{7},\text{ }\mathbf{0},\text{ }\mathbf{1} \right)\]are collinear.

Solution: If three points are collinear, then they lie on a line. Firstly let us calculate distance between the 3 points i.e. AB, BC and AC Calculating AB A ≡ \[\left( \mathbf{2},\text{...

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Fill in the blanks: (i) The x-axis and y-axis taken together determine a plane known as _______. (ii) The coordinates of points in the XY-plane are of the form _______. (iii) Coordinate planes divide the space into ______ octants.

Solution: (i) The x-axis and y-axis taken together determine a plane known as XY Plane. (ii) The coordinates of points in the XY-plane are of the form \[(x,y,0)\] (iii) Coordinate planes divide the...

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