NCERT Exemplar Solutions
Class 12 - Mathematics - Chapter 1: RELATIONS AND FUNCTIONS
Short Answer (S.A.)

Question. 1

Let \(A = \{a, b, c\}\) and the relation \(R\) be defined on \(A\) as follows: \(R = \{(a,a),(b,c),(a,b)\}\). Then, write minimum number of ordered pairs to be added in \(R\) to make \(R\) reflexive and transitive.

Answer:

(b,b), (c,c), (a,c)

Question. 2

Let \(D\) be the domain of the real valued function \(f\) defined by \(f(x) = \sqrt{25 - x^2}\). Then write \(D\).

Answer:

[-5, 5]

Question. 3

Let \(f, g : \mathbb{R} \to \mathbb{R}\) be defined by \(f(x) = 2x + 1\) and \(g(x) = x^2 - 2\). Find \(g \circ f\).

Answer:

4x² + 4x − 1

Question. 4

Let \(f : \mathbb{R} \to \mathbb{R}\) be defined by \(f(x) = 2x - 3\). Write \(f^{-1}\).

Answer:

\(f^{-1}(x) = \dfrac{x + 3}{2}\)

Question. 5

If \(A = \{a,b,c,d\}\) and the function \(f = \{(a,b),(b,d),(c,a),(d,c)\}\), write \(f^{-1}\).

Answer:

\{(b,a),(d,b),(a,c),(c,d)\}

Question. 6

If \(f : \mathbb{R} \to \mathbb{R}\) is defined by \(f(x) = x^2 - 3x + 2\), write \(f(f(x))\).

Answer:

\(x^4 - 6x^3 + 10x^2 - 3x\)

Question. 7

Is \(g = \{(1,1),(2,3),(3,5),(4,7)\}\) a function? If \(g(x) = \alpha x + \beta\), then what are the values of \(\alpha\) and \(\beta\)?

Answer:

\(\alpha = 2, \beta = -1\)

Question. 8

Are the following sets of ordered pairs functions? If so, examine whether the mapping is injective or surjective.
(i) \(\{(x,y): x \text{ is a person}, y \text{ is the mother of } x\}\)
(ii) \(\{(a,b): a \text{ is a person}, b \text{ is an ancestor of } a\}\)

Answer:

(i) Represents a function which is surjective but not injective.

(ii) Does not represent a function.

Question. 9

If mappings \(f\) and \(g\) are given by \(f = \{(1,2),(3,5),(4,1)\}\) and \(g = \{(2,3),(5,1),(1,3)\}\), write \(g \circ f\).

Answer:

\{(2,5),(5,2),(1,5)\}

Question. 10

Let \(C\) be the set of complex numbers. Prove that the mapping \(f:C \to \mathbb{R}\) defined by \(f(z)=|z|\) is neither one-one nor onto.

Answer:

Neither one-one nor onto.

Question. 11

Let the function \(f:\mathbb{R} \to \mathbb{R}\) be defined by \(f(x) = \cos x\). Show that \(f\) is neither one-one nor onto.

Answer:

Neither one-one nor onto.

Question. 12

Let \(X = \{1,2,3\}\) and \(Y = \{4,5\}\). Determine whether the following sets of \(X \times Y\) are functions from \(X\) to \(Y\):
(i) \(f = \{(1,4),(1,5),(2,4),(3,5)\}\)
(ii) \(g = \{(1,4),(2,4),(3,4)\}\)
(iii) \(h = \{(1,4),(2,5),(3,5)\}\)
(iv) \(k = \{(1,4),(2,5)\}\)

Answer:

(i) f is not a function

(ii) g is a function

(iii) h is a function

(iv) k is not a function

Question. 13

If functions \(f:A \to B\) and \(g:B \to A\) satisfy \(g \circ f = I_A\), show that \(f\) is one-one and \(g\) is onto.

Answer:

f is one-one and g is onto.

Question. 14

Let \(f:\mathbb{R} \to \mathbb{R}\) be defined by \(f(x) = \dfrac{1}{2 - \cos x}\). Find the range of \(f\).

Answer:

\([1/3, 1]\)

Question. 15

Let \(n\) be a fixed positive integer. Define a relation \(R\) in \(\mathbb{Z}\) as follows: for \(a,b \in \mathbb{Z}\), \(aRb\) iff \(a-b\) is divisible by \(n\). Show that \(R\) is an equivalence relation.

Answer:

R is an equivalence relation.

NCERT Exemplar Solutions Class 12 – Mathematics – Chapter 1: RELATIONS AND FUNCTIONS – Short Answer (S.A.) | Detailed Answers