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

Complete NCERT Solutions for problems given in INTRODUCTION TO THREE DIMENSIONAL GEOMETRY chapter in Class 11 Mathematics.

EXERCISE 11.1

Question. 1

A point is on the x-axis. What are its y-coordinate and z-coordinates?

Answer:

y and z - coordinates are zero

Question. 2

A point is in the XZ-plane. What can you say about its y-coordinate?

Answer:

y - coordinate is zero

Question. 3

Name the octants in which the following points lie:

(1, 2, 3), (4, −2, 3), (4, −2, −5), (4, 2, −5), (−4, 2, −5), (−4, 2, 5), (−3, −1, 6), (−2, −4, −7)

Answer:

I, IV, VIII, V, VI, II, III, VII

Question. 4

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.

Answer:

(i) XY - plane

(ii) (x, y, 0)

(iii) Eight

EXERCISE 11.2

Question. 1

Find the distance between the following pairs of points:

(i) \((2, 3, 5)\) and \((4, 3, 1)\)

(ii) \((-3, 7, 2)\) and \((2, 4, -1)\)

(iii) \((-1, 3, -4)\) and \((1, -3, 4)\)

(iv) \((2, -1, 3)\) and \((-2, 1, 3)\)

Answer:

(i) \(2\sqrt{5}\)

(ii) \(\sqrt{43}\)

(iii) \(2\sqrt{26}\)

(iv) \(2\sqrt{5}\)

Question. 2

Show that the points \((-2, 3, 5)\), \((1, 2, 3)\) and \((7, 0, -1)\) are collinear.

Question. 3

Verify the following:

(i) \((0, 7, -10), (1, 6, -6)\) and \((4, 9, -6)\) are the vertices of an isosceles triangle.

(ii) \((0, 7, 10), (-1, 6, 6)\) and \((-4, 9, 6)\) are the vertices of a right angled triangle.

(iii) \((-1, 2, 1), (1, -2, 5), (4, -7, 8)\) and \((2, -3, 4)\) are the vertices of a parallelogram.

Question. 4

Find the equation of the set of points which are equidistant from the points \((1, 2, 3)\) and \((3, 2, -1)\).

Answer:

\(x - 2z = 0\)

Question. 5

Find the equation of the set of points \(P\), the sum of whose distances from \(A(4, 0, 0)\) and \(B(-4, 0, 0)\) is equal to 10.

Answer:

\(9x^2 + 25y^2 + 25z^2 - 225 = 0\)

Miscellaneous Exercise on Chapter 11

Question. 1

Three vertices of a parallelogram ABCD are A(3, −1, 2), B(1, 2, −4) and C(−1, 1, 2). Find the coordinates of the fourth vertex.

Answer:

(1, −2, 8)

Question. 2

Find the lengths of the medians of the triangle with vertices A(0, 0, 6), B(0, 4, 0) and C(6, 0, 0).

Answer:

7, \(\sqrt{34}\), 7

Question. 3

If the origin is the centroid of the triangle PQR with vertices P(2a, 2, 6), Q(−4, 3b, −10) and R(8, 14, 2c), find the values of \(a\), \(b\) and \(c\).

Answer:

\(a = -2\), \(b = -\dfrac{16}{3}\), \(c = 2\)

Question. 4

If A and B be the points (3, 4, 5) and (−1, 3, −7), respectively, find the equation of the set of points P such that \(PA^2 + PB^2 = k^2\), where \(k\) is a constant.

Answer:

\(x^2 + y^2 + z^2 - 2x - 7y + 2z = \dfrac{k^2 - 109}{2}\)

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