NCERT Solutions
Class 11 - Mathematics - Chapter 1: SETS
EXERCISE 1.5

Question. 1

Let \( U = \{1, 2, 3, 4, 5, 6, 7, 8, 9\} \), \( A = \{1, 2, 3, 4\} \), \( B = \{2, 4, 6, 8\} \) and \( C = \{3, 4, 5, 6\} \). Find:

(i) \( A' \)  (ii) \( B' \)  (iii) \( (A \cup C)' \)  (iv) \( (A \cup B)' \)  (v) \( (A')' \)  (vi) \( (B - C)' \)

Answer:

(i) \( A' = \{5, 6, 7, 8, 9\} \)

(ii) \( B' = \{1, 3, 5, 7, 9\} \)

(iii) \( (A \cup C)' = \{7, 8, 9\} \)

(iv) \( (A \cup B)' = \{5, 7, 9\} \)

(v) \( (A')' = \{1, 2, 3, 4\} \)

(vi) \( (B - C)' = \{1, 3, 4, 5, 6, 7, 9\} \)

Question. 2

If \( U = \{a, b, c, d, e, f, g, h\} \), find the complements of the following sets:

(i) \( A = \{a, b, c\} \)  (ii) \( B = \{d, e, f, g\} \)  (iii) \( C = \{a, c, e, g\} \)  (iv) \( D = \{f, g, h, a\} \)

Answer:

(i) \( A' = \{d, e, f, g, h\} \)

(ii) \( B' = \{a, b, c, h\} \)

(iii) \( C' = \{b, d, f, h\} \)

(iv) \( D' = \{b, c, d, e\} \)

Question. 3

Taking the set of natural numbers as the universal set, write down the complements of the following sets:

(i) \( \{x : x \text{ is an even natural number}\} \)

(ii) \( \{x : x \text{ is an odd natural number}\} \)

(iii) \( \{x : x \text{ is a positive multiple of } 3\} \)

(iv) \( \{x : x \text{ is a prime number}\} \)

(v) \( \{x : x \text{ is a natural number divisible by } 3 \text{ and } 5\} \)

(vi) \( \{x : x \text{ is a perfect square}\} \)

(vii) \( \{x : x \text{ is a perfect cube}\} \)

(viii) \( \{x : x + 5 = 8\} \)

(ix) \( \{x : 2x + 5 = 9\} \)

(x) \( \{x : x \ge 7\} \)

(xi) \( \{x : x \in \mathbb{N} \text{ and } 2x + 1 > 10\} \)

Answer:

(i) \( \{x : x \text{ is an odd natural number}\} \)

(ii) \( \{x : x \text{ is an even natural number}\} \)

(iii) \( \{x : x \in \mathbb{N} \text{ and } x \text{ is not a multiple of } 3\} \)

(iv) \( \{x : x \text{ is a positive composite number or } x = 1\} \)

(v) \( \{x : x \text{ is a positive integer which is not divisible by } 3 \text{ or not divisible by } 5\} \)

(vi) \( \{x : x \in \mathbb{N} \text{ and } x \text{ is not a perfect square}\} \)

(vii) \( \{x : x \in \mathbb{N} \text{ and } x \text{ is not a perfect cube}\} \)

(viii) \( \{x : x \in \mathbb{N} \text{ and } x \ne 3\} \)

(ix) \( \{x : x \in \mathbb{N} \text{ and } x \ne 2\} \)

(x) \( \{x : x \in \mathbb{N} \text{ and } x < 7\} \)

(xi) \( \{x : x \in \mathbb{N} \text{ and } x \le \tfrac{9}{2}\} \)

Question. 4

If \( U = \{1, 2, 3, 4, 5, 6, 7, 8, 9\} \), \( A = \{2, 4, 6, 8\} \) and \( B = \{2, 3, 5, 7\} \), verify that:

(i) \( (A \cup B)' = A' \cap B' \)

(ii) \( (A \cap B)' = A' \cup B' \)

Question. 5

Draw appropriate Venn diagram for each of the following:

(i) \( (A \cup B)' \)

(ii) \( A' \cap B' \)

(iii) \( (A \cap B)' \)

(iv) \( A' \cup B' \)

Question. 6

Let \( U \) be the set of all triangles in a plane. If \( A \) is the set of all triangles with at least one angle different from \(60^{\circ}\), what is \( A' \)?

Answer:

\( A' \) is the set of all equilateral triangles.

Question. 7

Fill in the blanks to make each of the following a true statement:

(i) \( A \cup A' = \ldots \)

(ii) \( \varphi' \cap A = \ldots \)

(iii) \( A \cap A' = \ldots \)

(iv) \( U' \cap A = \ldots \)

Answer:

(i) \( U \)

(ii) \( A \)

(iii) \( \varphi \)

(iv) \( \varphi \)

NCERT Solutions Class 11 – Mathematics – Chapter 1: SETS – EXERCISE 1.5 | Detailed Answers