NCERT Exemplar Solutions
Class 11 - Mathematics
Chapter : INTRODUCTION TO THREE DIMENSIONAL GEOMETRY

Coordinate axes and coordinate planes, Coordinate of a point in space, Sign of coordinates of a point, Distance formula, Section formula.

Short Answer Type

Question. 1

In which octant do the points lie?

Answer:

(i) 1st octant

(ii) 4th octant

(iii) viiith octant

(iv) vth octant

(v) 2nd octant

(vi) 3rd octant

(vii) viiith octant

(viii) vith octant

Question. 2

Find the coordinates of the feet of perpendiculars from a point P on the xy, yz and zx-planes respectively for the given cases.

Answer:

(i) (3,0,0), (0,4,0), (0,0,2)

(ii) (−5,0,0), (0,3,0), (0,0,7)

(iii) (4,0,0), (0,−3,0), (0,0,5)

Question. 3

Find how far apart the points (2, 0, 0) and (−3, 0, 0) are.

Answer:

5

Question. 4

Find the distance from the origin to the point (6, 6, 7).

Answer:

11

Question. 5

Show that if \(x^2 + y^2 = 1\), then the point \((x, y, \sqrt{1 - x^2 - y^2})\) is at a distance 1 unit from the origin.

Answer:

1

Question. 6

Show that the points A (1, −1, 3), B (2, −4, 5) and (5, −13, 11) are collinear.

Answer:

(2, −4, 16)

Question. 7

Three consecutive vertices of a parallelogram ABCD are A (6, −2, 4), B (2, −4, −8), and C (−2, 2, 4). Find the coordinates of the fourth vertex.

Answer:

(−2, −2, −1)

Question. 8

Show that the triangle ABC with vertices A (0, 4, 1), B (2, 3, −1) and C (4, 5, 0) is right angled.

Answer:

(−3, −4, −7)

(7, 2, 5)

(−3, 12, 17)

Question. 9

Find the third vertex of a triangle whose centroid is origin and two vertices are (2, 4, 6) and (0, −2, −5).

Answer:

(4, 7, 6)

Question. 10

Find the centroid of a triangle the mid-point of whose sides are given as D (1, 2, −3), E (3, 0, 1), and F (−1, 1, −4).

Answer:

(4, −5, 1)

Question. 11

The mid-points of the sides of a triangle are (5, 7, 11), (0, 8, 5), and (2, 3, −1). Find its vertices.

Answer:

(3, −2, −1)

Question. 12

Three vertices of a parallelogram ABCD are A (1, 2, 3), B (−1, −2, −1), and C (2, 3, 2). Find the fourth vertex D.

Answer:

(7/2, 13/2, 9)

Question. 13

Find the coordinates of the points which trisect the line segment joining A (2, 1, −3) and B (5, −8, 3).

Answer:

2:1 externally

Question. 14

If the origin is the centroid of a triangle ABC having vertices A (a, 1, 3), B (−2, b, −5), and C (4, 7, c), find the values of a, b, c.

Answer:

a = −2, b = −8, c = 2

Question. 15

Let A (2, 2, −3), B (5, 6, 9) and C (2, 7, 9) be the vertices of a triangle. The internal bisector of angle A meets BC at point D. Find the coordinates of D.

Answer:

(7/2, 13/2, 9)

Question. 16

Show that the three points A (2, 3, 4), B (−1, 2, −3) and C (−4, 1, −10) are collinear and find the ratio in which C divides AB.

Answer:

2:1 externally

Question. 17

The distance of point P (3, 4, 5) from the yz-plane is?

Answer:

(7/2, 13/2, 9)

Long Answer Questions

Question. 18

Show that the three points A (2, 3, 4), B (−1, 2, −3) and C (−4, 1, −10) are collinear and find the ratio in which C divides AB.

Answer:

2:1 externally

Question. 19

The mid-point of the sides of a triangle are (1, 5, −1), (0, 4, −2) and (2, 3, 4). Find its vertices. Also find the centroid of the triangle.

Answer:

vertices are (3,4,5), (−1,6,−7), (1,2,3) and centroid is (1,4, 1/3)

Question. 20

Prove that the points (0, −1, −7), (2, 1, −9) and (6, 5, −13) are collinear. Find the ratio in which the first point divides the join of the other two.

Answer:

1:3 externally

Question. 21

What are the coordinates of the vertices of a cube whose edge is 2 units, one of whose vertices coincides with the origin and the three edges passing through the origin coincide with the positive direction of the axes through the origin?

Answer:

(2,0,0), (2,2,0), (0,2,0), (0,2,2), (2,0,2), (0,0,0), (2,2,2)

Objective Type Question

Choose the correct answer from the given four options:

Question.  22

The distance of point P(3, 4, 5) from the yz-plane is

(a)

3 units

(b)

4 units

(c)

5 units

(d)

550

Question.  23

What is the length of foot of perpendicular drawn from the point P(3, 4, 5) on y-axis

(a)

\(\sqrt{41}\)

(b)

\(\sqrt{34}\)

(c)

5

(d)

none of these

Question.  24

Distance of the point (3, 4, 5) from the origin (0, 0, 0) is

(a)

\(\sqrt{50}\)

(b)

3

(c)

4

(d)

5

Question.  25

If the distance between the points \((a,0,1)\) and \((0,1,2)\) is \(\sqrt{27}\), then the value of \(a\) is

(a)

5

(b)

\(\pm 5\)

(c)

-5

(d)

none of these

Question.  26

\(x\)-axis is the intersection of two planes

(a)

xy and xz

(b)

yz and zx

(c)

xy and yz

(d)

none of these

Question.  27

Equation of y-axis is considered as

(a)

\(x = 0,\; y = 0\)

(b)

\(y = 0,\; z = 0\)

(c)

\(z = 0,\; x = 0\)

(d)

none of these

Question.  28

The point \((-2, -3, -4)\) lies in the

(a)

First octant

(b)

Seventh octant

(c)

Second octant

(d)

Eighth octant

Question.  29

A plane is parallel to yz-plane so it is perpendicular to :

(a)

x-axis

(b)

y-axis

(c)

z-axis

(d)

none of these

Question.  30

The locus of a point for which \(y = 0,\; z = 0\) is

(a)

equation of x-axis

(b)

equation of y-axis

(c)

equation of z-axis

(d)

none of these

Question.  31

The locus of a point for which \(x = 0\) is

(a)

xy-plane

(b)

yz-plane

(c)

zx-plane

(d)

none of these

Question.  32

If a parallelepiped is formed by planes drawn through the points \((5,8,10)\) and \((3,6,8)\) parallel to the coordinate planes, then the length of diagonal of the parallelepiped is

(a)

\(2\sqrt{3}\)

(b)

\(3\sqrt{2}\)

(c)

\(\sqrt{2}\)

(d)

\(\sqrt{3}\)

Question.  33

\(L\) is the foot of the perpendicular drawn from a point \(P(3,4,5)\) on the xy-plane. The coordinates of point \(L\) are

(a)

(3, 0, 0)

(b)

(0, 4, 5)

(c)

(3, 0, 5)

(d)

none of these

Question.  34

\(L\) is the foot of the perpendicular drawn from the point \((3,4,5)\) on x-axis. The coordinates of \(L\) are

(a)

(3, 0, 0)

(b)

(0, 4, 0)

(c)

(0, 0, 5)

(d)

none of these

Fill in the Blanks

Question. 35

The three axes OX, OY, OZ determine ____.

Answer:

Three coordinates planes

Question. 36

The three planes determine a rectangular parallelepiped which has ______ of rectangular faces.

Answer:

Three pairs

Question. 37

The coordinates of a point are the perpendicular distance from the ______ on the respective axes.

Answer:

given point

Question. 38

The three coordinate planes divide the space into ______ parts.

Answer:

Eight

Question. 39

If a point P lies in yz-plane, then the coordinates of a point on yz-plane is of the form ______.

Answer:

(0, y, z)

Question. 40

The equation of yz-plane is ______.

Answer:

x = 0

Question. 41

If the point P lies on z-axis, then coordinates of P are of the form ______.

Answer:

(0, 0, z)

Question. 42

The equation of z-axis, are ______.

Answer:

x = 0 , y = 0

Question. 43

A line is parallel to xy-plane if all the points on the line have equal ______.

Answer:

z- coordinates

Question. 44

A line is parallel to x-axis if all the points on the line have equal ______.

Answer:

(y, z coordinates)

Question. 45

x = a represent a plane parallel to ______.

Answer:

yz-plane

Question. 46

The plane parallel to yz-plane is perpendicular to ______.

Answer:

x-axis

Question. 47

The length of the longest piece of a string that can be stretched straight in a rectangular room whose dimensions are 10, 13 and 8 units are ______.

Answer:

\(\sqrt{333}\)

Question. 48

If the distance between the points (a, 2, 1) and (1, –1, 1) is 5, then a ______.

Answer:

a = 5 or -3

Question. 49

If the mid-points of the sides of a triangle AB; BC; CA are D (1, 2, –3), E (3, 0, 1) and F (–1, 1, –4), then the centroid of the triangle ABC is ______.

Answer:

(1, 1, -2)

Match the Following

Question. 50

Match the items in Column A with Column B using the table below.

Column AColumn B

(a) In xy-plane

(i) Ist octant

(b) Point (2, 3, 4) lies in the

(ii) yz-plane

(c) Locus of the points having x coordinate 0 is

(iii) z-coordinate is zero

(d) A line is parallel to x-axis if and only if

(iv) z-axis

(e) If x = 0, y = 0 taken together will represent the

(v) plane parallel to xy-plane

(f) z = c represent the plane

(vi) if all the points on the line have equal y and z-coordinates

(g) Planes x = a, y = b represent the line

(vii) from the point on the respective

(h) Coordinates of a point are the distances from the origin to the feet of perpendiculars

(viii) parallel to z-axis

(i) A ball is the solid region in the space enclosed by a

(ix) disc

(j) Region in the plane enclosed by a circle is known as a

(x) sphere

Answer:

Column AMatched Item from Column B

(a) In xy-plane

(iii) z-coordinate is zero

(b) Point (2, 3, 4) lies in the

(i) Ist octant

(c) Locus of the points having x coordinate 0 is

(ii) yz-plane

(d) A line is parallel to x-axis if and only if

(vi) if all the points on the line have equal y and z-coordinates

(e) If x = 0, y = 0 taken together will represent the

(iv) z-axis

(f) z = c represent the plane

(v) plane parallel to xy-plane

(g) Planes x = a, y = b represent the line

(viii) parallel to z-axis

(h) Coordinates of a point are the distances from the origin to the feet of perpendiculars

(vii) from the point on the respective

(i) A ball is the solid region in the space enclosed by a

(x) sphere

(j) Region in the plane enclosed by a circle is known as a

(ix) disc

NCERT Exemplar Solutions Class 11 – Mathematics – Chapter : INTRODUCTION TO THREE DIMENSIONAL GEOMETRY | Detailed Answers