Maths MCQs for Class 12 with Answers Chapter 1 Relations and Functions

# Maths MCQs for Class 12 with Answers Chapter 1 Relations and Functions

## Relations and Functions Class 12 Maths MCQs Pdf

Question 1.
The function f : A → B defined by f(x) = 4x + 7, x ∈ R is
(a) one-one
(b) Many-one
(c) Odd
(d) Even
Answer:
(a) one-one

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Question 2.
The smallest integer function f(x) = [x] is
(a) One-one
(b) Many-one
(c) Both (a) & (b)
(d) None of these
Answer:
(b) Many-one

Question 3.
The function f : R → R defined by f(x) = 3 – 4x is
(a) Onto
(b) Not onto
(c) None one-one
(d) None of these
Answer:
(a) Onto

Question 4.
The number of bijective functions from set A to itself when A contains 106 elements is
(a) 106
(b) (106)2
(c) 106!
(d) 2106
Answer:
(c) 106!

Question 5.
If f(x) = (ax2 + b)3, then the function g such that f(g(x)) = g(f(x)) is given by
(a) $$g(x)=\left(\frac{b-x^{1 / 3}}{a}\right)$$
(b) $$g(x)=\frac{1}{\left(a x^{2}+b\right)^{3}}$$
(c) $$g(x)=\left(a x^{2}+b\right)^{1 / 3}$$
(d) $$g(x)=\left(\frac{x^{1 / 3}-b}{a}\right)^{1 / 2}$$
Answer:
(d) $$g(x)=\left(\frac{x^{1 / 3}-b}{a}\right)^{1 / 2}$$

Question 6.
If f : R → R, g : R → R and h : R → R is such that f(x) = x2, g(x) = tanx and h(x) = logx, then the value of [ho(gof)](x), if x = $$\frac{\sqrt{\pi}}{2}$$ will be
(a) 0
(b) 1
(c) -1
(d) 10
Answer:
(a) 0

Question 7.
If f : R → R and g : R → R defined by f(x) = 2x + 3 and g(x) = x2 + 7, then the value of x for which f(g(x)) = 25 is
(a) ±1
(b) ±2
(c) ±3
(d) ±4
Answer:
(b) ±2

Question 8.
Let f : N → R : f(x) = $$\frac{(2 x-1)}{2}$$ and g : Q → R : g(x) = x + 2 be two functions. Then, (gof) ($$\frac{3}{2}$$) is
(a) 3
(b) 1
(c) $$\frac{7}{2}$$
(d) None of these
Answer:
(a) 3

Question 9.
Let $$f(x)=\frac{x-1}{x+1}$$, then f(f(x)) is
(a) $$\frac{1}{x}$$
(b) $$-\frac{1}{x}$$
(c) $$\frac{1}{x+1}$$
(d) $$\frac{1}{x-1}$$
Answer:
(b) $$-\frac{1}{x}$$

Question 10.
If f(x) = $$1-\frac{1}{x}$$, then f(f($$\frac{1}{x}$$))
(a) $$\frac{1}{x}$$
(b) $$\frac{1}{1+x}$$
(c) $$\frac{x}{x-1}$$
(d) $$\frac{1}{x-1}$$
Answer:
(c) $$\frac{x}{x-1}$$

Question 11.
If f : R → R, g : R → R and h : R → R are such that f(x) = x2, g(x) = tan x and h(x) = log x, then the value of (go(foh)) (x), if x = 1 will be
(a) 0
(b) 1
(c) -1
(d) π
Answer:
(a) 0

Question 12.
If f(x) = $$\frac{3 x+2}{5 x-3}$$ then (fof)(x) is
(a) x
(b) -x
(c) f(x)
(d) -f(x)
Answer:
(a) x

Question 13.
If the binary operation * is defind on the set Q+ of all positive rational numbers by a * b = $$\frac{a b}{4}$$. Then, $$3 *\left(\frac{1}{5} * \frac{1}{2}\right)$$ is equal to
(a) $$\frac{3}{160}$$
(b) $$\frac{5}{160}$$
(c) $$\frac{3}{10}$$
(d) $$\frac{3}{40}$$
Answer:
(a) $$\frac{3}{160}$$

Question 14.
The number of binary operations that can be defined on a set of 2 elements is
(a) 8
(b) 4
(c) 16
(d) 64
Answer:
(c) 16

Question 15.
Let * be a binary operation on Q, defined by a * b = $$\frac{3 a b}{5}$$ is
(a) Commutative
(b) Associative
(c) Both (a) and (b)
(d) None of these
Answer:
(c) Both (a) and (b)

Question 16.
Let * be a binary operation on set Q of rational numbers defined as a * b = $$\frac{a b}{5}$$. Write the identity for *.
(a) 5
(b) 3
(c) 1
(d) 6
Answer:
(a) 5

Question 17.
For binary operation * defind on R – {1} such that a * b = $$\frac{a}{b+1}$$ is
(a) not associative
(b) not commutative
(c) commutative
(d) both (a) and (b)
Answer:
(d) both (a) and (b)

Question 18.
The binary operation * defind on set R, given by a * b = $$\frac{a+b}{2}$$ for all a,b ∈ R is
(a) commutative
(b) associative
(c) Both (a) and (b)
(d) None of these
Answer:
(a) commutative

Question 19.
Let A = N × N and * be the binary operation on A defined by (a, b) * (c, d) = (a + c, b + d). Then * is
(a) commutative
(b) associative
(c) Both (a) and (b)
(d) None of these
Answer:
(c) Both (a) and (b)

Question 20.
Find the identity element in the set I+ of all positive integers defined by a * b = a + b for all a, b ∈ I+.
(a) 1
(b) 2
(c) 3
(d) 0
Answer:
(d) 0

Question 21.
Let * be a binary operation on set Q – {1} defind by a * b = a + b – ab : a, b ∈ Q – {1}. Then * is
(a) Commutative
(b) Associative
(c) Both (a) and (b)
(d) None of these
Answer:
(c) Both (a) and (b)

Question 22.
The binary operation * defined on N by a * b = a + b + ab for all a, b ∈ N is
(a) commutative only
(b) associative only
(c) both commutative and associative
(d) none of these
Answer:
(c) both commutative and associative

Question 23.
The number of commutative binary operation that can be defined on a set of 2 elements is
(a) 8
(b) 6
(c) 4
(d) 2
Answer:
(d) 2

Question 24.
Let T be the set of all triangles in the Euclidean plane, and let a relation R on T be defined as aRb if a is congruent to b ∀ a, b ∈ T. Then R is
(a) reflexive but not transitive
(b) transitive but not symmetric
(c) equivalence
(d) None of these
Answer:
(c) equivalence

Question 25.
The maximum number of equivalence relations on the set A = {1, 2, 3} are
(a) 1
(b) 2
(c) 3
(d) 5
Answer:
(d) 5

Question 26.
Let us define a relation R in R as aRb if a ≥ b. Then R is
(a) an equivalence relation
(b) reflexive, transitive but not symmetric
(c) symmetric, transitive but not reflexive
(d) neither transitive nor reflexive but symmetric
Answer:
(b) reflexive, transitive but not symmetric

Question 27.
Let A = {1, 2, 3} and consider the relation R = {(1, 1), (2, 2), (3, 3), (1, 2), (2, 3), (1, 3)}. Then R is
(a) reflexive but not symmetric
(b) reflexive but not transitive
(c) symmetric and transitive
(d) neither symmetric, nor transitive
Answer:
(a) reflexive but not symmetric

Question 28.
The identity element for the binary operation * defined on Q – {0} as a * b = $$\frac{a b}{2}$$ ∀ a, b ∈ Q – {0) is
(a) 1
(b) 0
(c) 2
(d) None of these
Answer:
(c) 2

Question 29.
Let A = {1, 2, 3, …. n} and B = {a, b}. Then the number of surjections from A into B is
(a) $$^{n} P_{2}$$
(b) 2n – 2
(c) 2n – 1
(d) none of these
Answer:
(b) 2n – 2

Question 30.
Let f : R → R be defind by f(x) = $$\frac{1}{x}$$ ∀ x ∈ R. Then f is
(a) one-one
(b) onto
(c) bijective
(d) f is not defined
Answer:
(d) f is not defined

Question 31.
Which of the following functions from Z into Z are bijective?
(a) f(x) = x3
(b) f(x) = x + 2
(c) f(x) = 2x + 1
(d) f(x) = x2 + 1
Answer:
(b) f(x) = x + 2

Question 32.
Let f : R → R be the functions defined by f(x) = x3 + 5. Then f-1(x) is
(a) $$(x+5)^{\frac{1}{3}}$$
(b) $$(x-5)^{\frac{1}{3}}$$
(c) $$(5-x)^{\frac{1}{3}}$$
(d) 5 – x
Answer:
(b) $$(x-5)^{\frac{1}{3}}$$

Question 33.
Let f : R – {$$\frac{3}{5}$$} → R be defined by f(x) = $$\frac{3 x+2}{5 x-3}$$. Then
(a) f-1(x) = f(x)
(b) f-1(x) = -f(x)
(c) (fof) x = -x
(d) f-1(x) = $$\frac{1}{19}$$ f(x)
Answer:
(a) f-1(x) = f(x)

Question 34.
Let f : R → R be given by f(x) = tan x. Then f-1(1) is
(a) $$\frac{\pi}{4}$$
(b) {nπ + $$\frac{\pi}{4}$$; n ∈ Z}
(c) Does not exist
(d) None of these
Answer:
(b) {nπ + $$\frac{\pi}{4}$$; n ∈ Z}

Question 35.
Let R be a relation on the set N of natural numbers denoted by nRm ⇔ n is a factor of m (i.e. n | m). Then, R is
(a) Reflexive and symmetric
(b) Transitive and symmetric
(c) Equivalence
(d) Reflexive, transitive but not symmetric
Answer:
(d) Reflexive, transitive but not symmetric

Question 36.
Let S = {1, 2, 3, 4, 5} and let A = S × S. Define the relation R on A as follows:
(a, b) R (c, d) iff ad = cb. Then, R is
(a) reflexive only
(b) Symmetric only
(c) Transitive only
(d) Equivalence relation
Answer:
(d) Equivalence relation

Question 37.
Let R be the relation “is congruent to” on the set of all triangles in a plane is
(a) reflexive
(b) symmetric
(c) symmetric and reflexive
(d) equivalence
Answer:
(d) equivalence

Question 38.
Total number of equivalence relations defined in the set S = {a, b, c} is
(a) 5
(b) 3!
(c) 23
(d) 33
Answer:
(a) 5

Question 39.
The relation R is defined on the set of natural numbers as {(a, b) : a = 2b}. Then, R-1 is given by
(a) {(2, 1), (4, 2), (6, 3),….}
(b) {(1, 2), (2, 4), (3, 6), ……..}
(c) R-1 is not defiend
(d) None of these
Answer:
(b) {(1, 2), (2, 4), (3, 6), ……..}

Question 40.
Let X = {-1, 0, 1}, Y = {0, 2} and a function f : X → Y defiend by y = 2x4, is
(a) one-one onto
(b) one-one into
(c) many-one onto
(d) many-one into
Answer:
(c) many-one onto

Question 41.
Let f : R → R be a function defined by $$f(x)=\frac{e^{|x|}-e^{-x}}{e^{x}+e^{-x}}$$ then f(x) is
(a) one-one onto
(b) one-one but not onto
(c) onto but not one-one
(d) None of these
Answer:
(d) None of these

Question 42.
Let g(x) = x2 – 4x – 5, then
(a) g is one-one on R
(b) g is not one-one on R
(c) g is bijective on R
(d) None of these
Answer:
(b) g is not one-one on R

Question 43.
Let A = R – {3}, B = R – {1}. Let f : A → B be defined by $$f(x)=\frac{x-2}{x-3}$$. Then,
(a) f is bijective
(b) f is one-one but not onto
(c) f is onto but not one-one
(d) None of these
Answer:
(a) f is bijective

Question 44.
The mapping f : N → N is given by f(n) = 1 + n2, n ∈ N when N is the set of natural numbers is
(a) one-one and onto
(b) onto but not one-one
(c) one-one but not onto
(d) neither one-one nor onto
Answer:
(c) one-one but not onto

Question 45.
The function f : R → R given by f(x) = x3 – 1 is
(a) a one-one function
(b) an onto function
(c) a bijection
(d) neither one-one nor onto
Answer:
(c) a bijection

Question 46.
Let f : [0, ∞) → [0, 2] be defined by $$f(x)=\frac{2 x}{1+x}$$, then f is
(a) one-one but not onto
(b) onto but not one-one
(c) both one-one and onto
(d) neither one-one nor onto
Answer:
(a) one-one but not onto

Question 47.
If N be the set of all-natural numbers, consider f : N → N such that f(x) = 2x, ∀ x ∈ N, then f is
(a) one-one onto
(b) one-one into
(c) many-one onto
(d) None of these
Answer:
(b) one-one into

Question 48.
Let A = {x : -1 ≤ x ≤ 1} and f : A → A is a function defined by f(x) = x |x| then f is
(a) a bijection
(b) injection but not surjection
(c) surjection but not injection
(d) neither injection nor surjection
Answer:
(a) a bijection

Question 49.
Let f : R → R be a function defined by f(x) = x3 + 4, then f is
(a) injective
(b) surjective
(c) bijective
(d) none of these
Answer:
(c) bijective

Question 50.
If f(x) = (ax2 – b)3, then the function g such that f{g(x)} = g{f(x)} is given by
(a) $$g(x)=\left(\frac{b-x^{1 / 3}}{a}\right)^{1 / 2}$$
(b) $$g(x)=\frac{1}{\left(a x^{2}+b\right)^{3}}$$
(c) $$g(x)=\left(a x^{2}+b\right)^{1 / 3}$$
(d) $$g(x)=\left(\frac{x^{1 / 3}+b}{a}\right)^{1 / 2}$$
Answer:
(d) $$g(x)=\left(\frac{x^{1 / 3}+b}{a}\right)^{1 / 2}$$

Question 51.
If f : [1, ∞) → [2, ∞) is given by f(x) = x + $$\frac{1}{x}$$, then f-1 equals to
(a) $$\frac{x+\sqrt{x^{2}-4}}{2}$$
(b) $$\frac{x}{1+x^{2}}$$
(c) $$\frac{x-\sqrt{x^{2}-4}}{2}$$
(d) $$1+\sqrt{x^{2}-4}$$
Answer:
(a) $$\frac{x+\sqrt{x^{2}-4}}{2}$$

Question 52.
Let f(x) = x2 – x + 1, x ≥ $$\frac{1}{2}$$, then the solution of the equation f(x) = f-1(x) is
(a) x = 1
(b) x = 2
(c) x = $$\frac{1}{2}$$
(d) None of these
Answer:
(a) x = 1

Question 53.
Which one of the following function is not invertible?
(a) f : R → R, f(x) = 3x + 1
(b) f : R → [0, ∞), f(x) = x2
(c) f : R+ → R+, f(x) = $$\frac{1}{x^{3}}$$
(d) None of these
Answer:
(d) None of these

Question 54.
The inverse of the function $$y=\frac{10^{x}-10^{-x}}{10^{x}+10^{-x}}$$ is
(a) $$\log _{10}(2-x)$$
(b) $$\frac{1}{2} \log _{10}\left(\frac{1+x}{1-x}\right)$$
(c) $$\frac{1}{2} \log _{10}(2 x-1)$$
(d) $$\frac{1}{4} \log \left(\frac{2 x}{2-x}\right)$$
Answer:
(b) $$\frac{1}{2} \log _{10}\left(\frac{1+x}{1-x}\right)$$

Question 55.
If f : R → R defind by f(x) = $$\frac{2 x-7}{4}$$ is an invertible function, then find f-1.
(a) $$\frac{4 x+5}{2}$$
(b) $$\frac{4 x+7}{2}$$
(c) $$\frac{3 x+2}{2}$$
(d) $$\frac{9 x+3}{5}$$
Answer:
(b) $$\frac{4 x+7}{2}$$

Question 56.
Consider the function f in A = R – {$$\frac{2}{3}$$} defiend as $$f(x)=\frac{4 x+3}{6 x-4}$$. Find f-1.
(a) $$\frac{3+4 x}{6 x-4}$$
(b) $$\frac{6 x-4}{3+4 x}$$
(c) $$\frac{3-4 x}{6 x-4}$$
(d) $$\frac{9+2 x}{6 x-4}$$
Answer:
(a) $$\frac{3+4 x}{6 x-4}$$

Question 57.
If f is an invertible function defined as f(x) = $$\frac{3 x-4}{5}$$, then f-1(x) is
(a) 5x + 3
(b) 5x + 4
(c) $$\frac{5 x+4}{3}$$
(d) $$\frac{3 x+2}{3}$$
Answer:
(c) $$\frac{5 x+4}{3}$$

Question 58.
If f : R → R defined by f(x) = $$\frac{3 x+5}{2}$$ is an invertible function, then find f-1.
(a) $$\frac{2 x-5}{3}$$
(b) $$\frac{x-5}{3}$$
(c) $$\frac{5 x-2}{3}$$
(d) $$\frac{x-2}{3}$$
Answer:
(a) $$\frac{2 x-5}{3}$$

Question 59.
Let f : R → R, g : R → R be two functions such that f(x) = 2x – 3, g(x) = x3 + 5. The function (fog)-1 (x) is equal to
(a) $$\left(\frac{x+7}{2}\right)^{1 / 3}$$
(b) $$\left(x-\frac{7}{2}\right)^{1 / 3}$$
(c) $$\left(\frac{x-2}{7}\right)^{1 / 3}$$
(d) $$\left(\frac{x-7}{2}\right)^{1 / 3}$$
Answer:
(d) $$\left(\frac{x-7}{2}\right)^{1 / 3}$$

Question 60.
Let * be a binary operation on set of integers I, defined by a * b = a + b – 3, then find the value of 3 * 4.
(a) 2
(b) 4
(c) 7
(d) 6
Answer:
(c) 7

Question 61.
If * is a binary operation on set of integers I defined by a * b = 3a + 4b – 2, then find the value of 4 * 5.
(a) 35
(b) 30
(c) 25
(d) 29
Answer:
(b) 30

Question 62.
Let * be the binary operation on N given by a * b = HCF (a, b) where, a, b ∈ N. Find the value of 22 * 4.
(a) 1
(b) 2
(c) 3
(d) 4
Answer:
(b) 2

Question 63.
Consider the binary operation * on Q defind by a * b = a + 12b + ab for a, b ∈ Q. Find 2 * $$\frac{1}{3}$$
(a) $$\frac{20}{3}$$
(b) 4
(c) 18
(d) $$\frac{16}{3}$$
Answer:
(a) $$\frac{20}{3}$$

Question 64.
The domain of the function $$f(x)=\frac{1}{\sqrt{\{\sin x\}+\{\sin (\pi+x)\}}}$$ where {.} denotes fractional part, is
(a) [0, π] (b) (2n + 1) π/2, n ∈ Z
(c) (0, π)
(d) None of these
Answer:
(d) None of these

Question 65.
Range of $$f(x)=\sqrt{(1-\cos x) \sqrt{(1-\cos x) \sqrt{(1-\cos x) \ldots \ldots \infty}}}$$
(a) [0, 1] (b) (0, 1)
(c) [0, 2] (d) (0, 2)
Answer:
(c) [0, 2]

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