Chapter-1. Relations and Functions

Number of binary operations on the set {a, b} are

(A) 10 (B) 16 (C) 20 (D) 8

Let f: R Ã¢â€ ’ R be the Signum Function defined as

and g: R Ã¢â€ ’ R be the Greatest Integer Function given by g(x) = [x], where [x] is greatest integer less than or equal to x. Then does fog andgof coincide in (0, 1]?

Let A = {1, 2, 3}. Then number of equivalence relations containing (1, 2) is

(A) 1 (B) 2 (C) 3 (D) 4

Let A = {1, 2, 3}. Then number of relations containing (1, 2) and (1, 3) which are reflexive and symmetric but not transitive is

(A) 1 (B) 2 (C) 3 (D) 4

Let A = { - 1, 0, 1, 2}, B = { - 4, - 2, 0, 2} and f, g: A Ã¢â€ ’ B be functions defined by f(x) = x² - x, x ∈ A and.Are fand g equal?

Justify your answer. (Hint: One may note that two function f: A Ã¢â€ ’ B and g: A Ã¢â€ ’ B such that f(a) = g(a) "a ∈A, are called equal functions).

Define a binary operation *on the set {0, 1, 2, 3, 4, 5} as

Show that zero is the identity for this operation and each element a ≠ 0 of the set is invertible with 6 - a being the inverse of a.

Given a non-empty set X, let *: P(X) x P(X) → P(X) be defined as A * B = (A - B) ∪ (B - A), " A, B ∈ P(X). Show that the empty set Φ is the identity for the operation * and all the elements A of P(X) are invertible with A^-1 = A. (Hint: (A - Φ) ∪ (Φ - A) = A and (A - A) ∪ (A - A) = A * A = Φ).

Consider the binary operations*: R ×R Ã¢â€ ’ and o: R × R Ã¢â€ ’ R defined as  and a o b = a, "a, b ∈ R. Show that * is commutative but not associative, o is associative but not commutative. Further, show that "a, b, c ∈ R, a*(b o c) = (a * b) o (a * c). [If it is so, we say that the operation * distributes over the operation o]. Does o distribute over *? Justify your answer.

Let S = {a, b, c} and T = {1, 2, 3}. Find F^-1 of the following functions F from S to T, if it exists.

(i) F= {(a, 3), (b, 2), (c, 1)} (ii) F= {(a, 2), (b, 1), (c, 1)}

Find the number of all onto functions from the set {1, 2, 3, … , n) to itself.

Given a non-empty set X, consider the binary operation *: P(X) x P(X) → P(X) given by A * B = A ∩ B " A, B in P(X) is the power set of X. Show that X is the identity element for this operation and X is the only invertible element in P(X) with respect to the operation*.

Given a non empty set X, consider P(X) which is the set of all subsets of X.

Define the relation R in P(X) as follows:

For subsets A, B in P(X), ARB if and only if A ⊂ B. Is R an equivalence relation on P(X)? Justify you answer:

Given examples of two functions f: N Ã¢â€ ’ N and g: N Ã¢â€ ’ N such that gof is onto but f is not onto.

(Hint: Consider f(x) = x + 1 and

Give examples of two functions f: N Ã¢â€ ’ Z and g: Z Ã¢â€ ’ Z such that g o f is injective but g is not injective.

(Hint: Consider f(x) = x and g(x) =)

Show that the function f: R → R given by f(x) = x³ is injective.

Show that function f: R Ã¢â€ ’ {x ∈ R: - 1 < x < 1} defined by f(x) =, x ∈R is one-one and onto function.

Let f: W → W be defined as f(n) = n - 1, if is odd and f(n) = n + 1, if n is even. Show that f is invertible. Find the inverse of f. Here, W is the set of all whole numbers.

Let f: R → R be defined as f(x) = 10x + 7. Find the function g: R → R such that g o f = f o g = 1_R.

Consider a binary operation * on N defined as a * b = a³ + b³. Choose the correct answer.

(A) Is * both associative and commutative?

(B) Is * commutative but not associative?

(C) Is * associative but not commutative?

(D) Is * neither commutative nor associative?

State whether the following statements are true or false. Justify.

(i) For an arbitrary binary operation * on a set N, a * a = a  a * N.

(ii) If * is a commutative binary operation on N, then a * (b * c) = (c * b) * a

Let A = N x N and * be the binary operation on A defined by

(a, b) * (c, d) = (a + c, b + d)

Show that * is commutative and associative. Find the identity element for * on A, if any.

Find which of the operations given above has identity.

Let * be a binary operation on the set Q of rational numbers as follows:

(i) a * b = a - b (ii) a * b = a² + b²

(iii) a * b = a + ab (iv) a * b = (a - b)²

(v) (vi) a * b = ab2

Find which of the binary operations are commutative and which are associative.

Let * be the binary operation on N defined by a * b = H.C.F. of a and b. Is * commutative? Is * associative? Does there exist identity for this binary operation on N?

Is * defined on the set {1, 2, 3, 4, 5} by a * b = L.C.M. of a and b a binary operation? Justify your answer.

Let * be the binary operation on N given by a * b = L.C.M. of a and b. Find

(i) 5 * 7, 20 * 16 (ii) Is * commutative?

(iii) Is * associative? (iv) Find the identity of * in N

(v) Which elements of N are invertible for the operation *?

Let*”² be the binary operation on the set {1, 2, 3, 4, 5} defined by a *”² b = H.C.F. of a and b. Is the operation *”² same as the operation *defined in Exercise 4 above? Justify your answer.

consider a binary operation * on the set {1, 2, 3, 4, 5} given by the following multiplication table.

(i) Compute (2 * 3) * 4 and 2 * (3 * 4)

(ii) Is * commutative?

(iii) Compute (2 * 3) * (4 * 5).

(Hint: use the following table)

Consider the binary operation ∨ on the set {1, 2, 3, 4, 5} defined by a ∨b = min {a, b}. Write the operation table of the operation∨.

For each binary operation * defined below, determine whether * is commutative or associative.

(i) On Z, define a * b = a - b

(ii) On Q, define a * b = ab + 1

(iii) On Q, define a * b 

(iv) On Z⁺, define a * b = 2^ab

(v) On Z⁺, define a * b = a^b

(vi) On R - { - 1}, define 

Determine whether or not each of the definition of given below gives a binary operation. In the event that * is not a binary operation, give justification for this.

(i) On Z⁺, define * by a * b = a - b

(ii) On Z⁺, define * by a * b = ab

(iii) On R, define * by a * b = ab²

(iv) On Z⁺, define * by a * b = |a - b|

(v) On Z⁺, define * by a * b = a

:  

Letbe a function defined as. The inverse of fis map g: Range

(A)  (B) 

(C)  (D) 

If f: R Ã¢â€ ’ R be given by, then fof(x) is

(A)  (B) x³ (C) x (D) (3 - x³)

Let f: X → Y be an invertible function. Show that the inverse of f^-1 is f, i.e.,

(f^-1)^-1 = f.

Consider f: {1, 2, 3} → {a, b, c} given by f(1) = a, f(2) = b and f(3) = c. Find f^-1and show that (f^-1)^-1= f.

Let f: X → Y be an invertible function. Show that f has unique inverse.

(Hint: suppose g₁ and g₂ are two inverses of f. Then for all y ∈ Y,

fog₁(y) = I_Y(y) = fog₂(y). Use one-one ness of f).

Consider f: R₊→ [ - 5, ∞) given by f(x) = 9x²+ 6x - 5. Show that fis invertible with.

Consider f: R₊ Ã¢â€ ’ [4, ∞) given by f(x) = x²+ 4. Show that fis invertible with the inverse f ^{- 1}of given f by, where R₊is the set of all non-negative real numbers.

Consider f: R → Rgiven by f(x) = 4x + 3. Show that fis invertible. Find the inverse of f.

Show that f: [ - 1, 1] → R, given byis one-one. Find the inverse of the function f: [ - 1, 1] → Range f.

(Hint: For y ∈Range f, y =, for some x in [ - 1, 1], i.e.,)

State with reason whether following functions have inverse

(i) f: {1, 2, 3, 4} → {10} with

f = {(1, 10), (2, 10), (3, 10), (4, 10)}

(ii) g: {5, 6, 7, 8} → {1, 2, 3, 4} with

g = {(5, 4), (6, 3), (7, 4), (8, 2)}

(iii) h: {2, 3, 4, 5} → {7, 9, 11, 13} with

h = {(2, 7), (3, 9), (4, 11), (5, 13)}

If, show that f o f(x) = x, for all. What is the inverse of f?

Find gof and fog, if

(i) 

(ii) 

Let f, g and h be functions from R to R. Show that

Let f: {1, 3, 4} → {1, 2, 5} and g: {1, 2, 5} → {1, 3} be given by f = {(1, 2), (3, 5), (4, 1)} and g = {(1, 3), (2, 3), (5, 1)}. Write down gof.

Let f: R → R be defined as f(x) = 3x. Choose the correct answer.

(A) f is one-one onto (B) f is many-one onto

(C) f is one-one but not onto (D) f is neither one-one nor onto

Let f: R → R be defined as f(x) = x⁴. Choose the correct answer.

(A) f is one-one onto (B) f is many-one onto

(C) f is one-one but not onto (D) f is neither one-one nor onto

Let A = R - {3} and B = R - {1}. Consider the function f: A → B defined by

. Is f one-one and onto? Justify your answer.

Let f: N Ã¢â€ ’ N be defined by

State whether the function f is bijective. Justify your answer.

Let A and B be sets. Show that f: A x B → B x A such that (a, b) = (b, a) is bijective function.

In each of the following cases, state whether the function is one-one, onto or bijective. Justify your answer.

(i) f: R → R defined by f(x) = 3 - 4x

(ii) f: R → R defined by f(x) = 1 + x²

Let A = {1, 2, 3}, B = {4, 5, 6, 7} and let f = {(1, 4), (2, 5), (3, 6)} be a function from A to B. Show that f is one-one.

Show that the Signum Function f: R Ã¢â€ ’ R, given by

is neither one-one nor onto.

Prove that the Greatest Integer Function f: R → R given by f(x) = [x], is neither one-once nor onto, where [x] denotes the greatest integer less than or equal to x.

Check the injectivity and surjectivity of the following functions:

(i) f: N → N given by f(x) = x²

(ii) f: Z → Z given by f(x) = x²

(iii) f: R → R given by f(x) = x²

(iv) f: N → N given by f(x) = x³

(v) f: Z → Z given by f(x) = x³

Show that the function f: R* Ã¢â€ ’ R* defined byis one-one and onto, where R* is the set of all non-zero real numbers. Is the result true, if the domain R* is replaced by N with co-domain being same as R*?

Let R be the relation in the set N given by R = {(a, b): a = b - 2, b > 6}. Choose the correct answer.

(A) (2, 4) ∈ R (B) (3, 8) ∈R (C) (6, 8) ∈R (D) (8, 7) ∈ R

Let R be the relation in the set {1, 2, 3, 4} given by R = {(1, 2), (2, 2), (1, 1), (4, 4), (1, 3), (3, 3), (3, 2)}. Choose the correct answer.

(A) R is reflexive and symmetric but not transitive.

(B) R is reflexive and transitive but not symmetric.

(C) R is symmetric and transitive but not reflexive.

(D) R is an equivalence relation.

Let L be the set of all lines in XY plane and R be the relation in L defined as R = {(L₁, L₂): L₁ is parallel to L₂}. Show that R is an equivalence relation. Find the set of all lines related to the line y = 2x + 4.

Show that the relation R defined in the set A of all polygons as R = {(P₁, P₂): P₁ and P₂ have same number of sides}, is an equivalence relation. What is the set of all elements in A related to the right angle triangle T with sides 3, 4 and 5?

Show that the relation R defined in the set A of all triangles as R = {(T₁, T₂): T₁ is similar to T₂}, is equivalence relation. Consider three right angle triangles T₁ with sides 3, 4, 5, T₂ with sides 5, 12, 13 and T₃ with sides 6, 8, 10. Which triangles among T₁, T₂ and T₃ are related?

Show that the relation R in the set A of points in a plane given by R = {(P, Q): distance of the point P from the origin is same as the distance of the point Q from the origin}, is an equivalence relation. Further, show that the set of all point related to a point P ≠ (0, 0) is the circle passing through P with origin as centre.

Given an example of a relation. Which is

(i) Symmetric but neither reflexive nor transitive.

(ii) Transitive but neither reflexive nor symmetric.

(iii) Reflexive and symmetric but not transitive.

(iv) Reflexive and transitive but not symmetric.

(v) Symmetric and transitive but not reflexive.

Show that each of the relation R in the set, given by

(i) 

(ii) 

is an equivalence relation. Find the set of all elements related to 1 in each case.

Show that the relation R in the set A = {1, 2, 3, 4, 5} given by

, is an equivalence relation. Show that all the elements of {1, 3, 5} are related to each other and all the elements of {2, 4} are related to each other. But no element of {1, 3, 5} is related to any element of {2, 4}.

Show that the relation R in the set A of all the books in a library of a college, given by R = {(x, y): x and y have same number of pages} is an equivalence relation.

Show that the relation R in the set {1, 2, 3} given by R = {(1, 2), (2, 1)} is symmetric but neither reflexive nor transitive.

Check whether the relation R in R defined as R = {(a, b): a ≤ b³} is reflexive, symmetric or transitive.

Show that the relation R in R defined as R = {(a, b): a ≤ b}, is reflexive and transitive but not symmetric.

Check whether the relation R defined in the set {1, 2, 3, 4, 5, 6} as

R = {(a, b): b = a + 1} is reflexive, symmetric or transitive.

Show that the relation R in the set R of real numbers, defined as

R = {(a, b): a ≤ b²} is neither reflexive nor symmetric nor transitive.

Determine whether each of the following relations are reflexive, symmetric and transitive:

(i)Relation R in the set A = {1, 2, 3…13, 14} defined as

R = {(x, y): 3x - y = 0}

(ii) Relation R in the set N of natural numbers defined as

R = {(x, y): y = x + 5 and x < 4}

(iii) Relation R in the set A = {1, 2, 3, 4, 5, 6} as

R = {(x, y): y is divisible by x}

(iv) Relation R in the set Z of all integers defined as

R = {(x, y): x - y is as integer}

(v) Relation R in the set A of human beings in a town at a particular time given by

(a) R = {(x, y): x and y work at the same place}

(b) R = {(x, y): x and y live in the same locality}

(c) R = {(x, y): x is exactly 7 cm taller than y}

(d) R = {(x, y): x is wife of y}

(e) R = {(x, y): x is father of y}