NCERT solutions for Class 12 Maths chapter 1 - Relations and Functions [Latest edition]

Determine whether  the following relations are reflective, symmetric and transitive:

Relation R in the set  A  = {1, 2, 3...13, 14} defined as R = {(x,y):3x - y = 0}

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

Relation R in the set N of natural numbers defined as

R = {(x, y): y = x + 5 and x < 4}

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

Relation R in the set A = {1, 2, 3, 4, 5, 6} as R = {(x, y): y is divisible by x}

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

Relation R in the set Z of all integers defined as

R = {(x, y): x − y is as integer}

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}

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.

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

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

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.

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 A = {1, 2, 3, 4, 5} given by `R = {(a,b) : |a-b| " is even"}` 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 each of the relation R in the set A= {x in Z : 0 <= x <= 12} given by R = {(a,b):|a-b| is a multiple of 4}

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

Show that each of the relation R in the set `A = {x =Z: 0 <= <= 12 }`  given by `R = {(a,b) : a= b}

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

Given an example of a relation. Which is Symmetric but neither reflexive nor transitive.

Given an example of a relation. Which is Transitive but neither reflexive nor symmetric.

Given an example of a relation. Which is  Reflexive and symmetric but not transitive.

Given an example of a relation. Which is Reflexive and transitive but not symmetric.

Given an example of a relation. Which is Symmetric and transitive but not reflexive.

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.

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, T₂and T₃ are related?

Show that the relation R defined in the set A of all polygons as R = {(P₁, P₂): P₁ and P₂have 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?

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.

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 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

Show that the function f: R_* → R_* defined by `f(x) = 1/x` is 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?

Check the injectivity and surjectivity of the following functions:

f: N → N given by f(x) = x²

Check the injectivity and surjectivity of the given functions: f: Z → Z given by f(x) = x²

Check the injectivity and surjectivity of the given functions:  f: R → R given by f(x) = x²

Check the injectivity and surjectivity of the following functions: f: N → N given by f(x) = x³

Check the injectivity and surjectivity of the following functions: f: Z → Z given by f(x) = x³

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.

Show that the Modulus Function f: R → R given by `f(x) = |x|` is neither one-one nor onto, where `|x|` is x, if xis positive or 0 and |x|  is − x, if x is negative.

Show that the Signum Function f: R → R, given by

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.

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

f: R → R defined by f(x) = 3 − 4x

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

f: R → R defined by f(x) = 1 + x²

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

Let f: N → N be defined by f(n) = `{((n+1)/2, "if n is odd"),(,"   for all n ∈ N"), (n/2, if "n is even"):}`

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

Let A = R − {3} and B = R − {1}. Consider the function f: A → B defined by `f(x) = ((x- 2)/(x -3))`. Is f one-one and onto? Justify your answer.

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 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: {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, g and h be functions from R to R. Show that

`(f + g)oh = foh + goh`

`(f.g)oh = (foh).(goh)`

Find gof and fog, if  f(x) = |x| and g(x) = |5x - 2|

Find gof and fog, if `f(x) = 8x^3` and `g(x) = x^(1/3)`

if f(x) = `(4x + 3)/(6x - 4), x ≠  2/3` show that fof(x) = x, for all x ≠ 2/3 . What is the inverse of f?

State with reason whether following functions have inverse

f: {1, 2, 3, 4} → {10} with

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

State with reason whether following functions have inverse g: {5, 6, 7, 8} → {1, 2, 3, 4} with g = {(5, 4), (6, 3), (7, 4), (8, 2)}

State with reason whether following functions have inverse h: {2, 3, 4, 5} → {7, 9, 11, 13} with h = {(2, 7), (3, 9), (4, 11), (5, 13)}

Show that f: [−1, 1] → R, given by f(x) = `x/(x + 2)`  is one-one. Find the inverse of the function f: [−1, 1] → Range f.

(Hint: For y in Range f, y = `f(x) = x/(x +2)` for some x in [-1, 1] ie x = `2y/(1-y)`

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

Consider f: R₊ → [4, ∞) given by f(x) = x² + 4. Show that f is invertible with the inverse f⁻¹ of given f by `f^(-1) (y) = sqrt(y - 4)` where R₊ is the set of all non-negative real numbers.

Consider f: R₊ → [−5, ∞) given by f(x) = 9x² + 6x − 5. Show that f is invertible with `f^(-1)(y) = ((sqrt(y +6) - 1)/3)`

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

Let f: X → Y be an invertible function. Show that the inverse of f⁻¹ is f, i.e., (f⁻¹)⁻¹ = f.

If f: R → R be given by `f(x) = (3 - x^3)^(1/3)` , then fof(x) is 

(A) `1/(x^3)`

(B) x³

(C) x

(D) (3 − x³)

Let `f:R - {-4/3} -> R` be a function defined as `f(x) = (4x)/(3x + 4)`. The inverse of f is map g Range `f -> R -{- 4/3}`

(A) `g(y) = (3y)/(3-4y)`

(B) `g(y) = (4y)/(4 - 3y)`

(C) `g(y) = (4y)/(3 - 4y)` 

(D) `g(y) = (3y)/(4 - 3y)`

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

On Z+, define ∗ by a ∗ b = a – b

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

On Z⁺, define * by a * b = ab

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.

On R, define * by a * b = ab²

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.

On Z⁺, define * by a * b = |a − b|

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.

On Z⁺, define * by a * b = a

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

On Z, define a * b = a − b

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

On Q, define a * b = ab + 1

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

On Q, define a * b  = `(ab)/2`

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

On Z⁺, define a * b = 2^ab

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

On Z⁺, define a * b = a^b

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

On R − {−1}, define `a*b = a/(b+1)`

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∨.

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)

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

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 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) a * b = ab/4

(vi) a * b = ab²

Find which of the operations given above has identity.

Let A = N × 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.

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

For an arbitrary binary operation * on a set N, a * a = ∀ a  a * N.

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

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

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?

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.

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.

If f: R → R is defined by f(x) = x² − 3x + 2, find f(f(x)).

Show that function f: R `rightarrow` {x ∈ R : −1 < x < 1} defined by f(x) = `x/(1 + |x|)`, x ∈ R is one-one and onto function.

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

Give examples of two functions f: N → Z and g: Z → Z such that g o f is injective but gis not injective.

(Hint: Consider f(x) = x and g(x) =|x|)

Given examples of two functions f: N → N and g: N → N such that gof is onto but f is not onto.

(Hint: Consider f(x) = x + 1 and `g(x) = {(x-1, ifx >1),(1, if x = 1):}`

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 a non-empty set X, consider the binary operation *: P(X) × P(X) → P(X) given by A * B = A ∩ B &mnForE; 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*.

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

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.

F = {(a, 3), (b, 2), (c, 1)} 

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.

F = {(a, 2), (b, 1), (c, 1)}

Consider the binary operations*: R ×R → and o: R × R → R defined as a * b = |a - b| and ao b = a, &mnForE;a, b ∈ R. Show that * is commutative but not associative, o is associative but not commutative. Further, show that &mnForE;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.

Given a non-empty set X, let *: P(X) × P(X) → P(X) be defined as A * B = (A − B) ∪ (B −A), &mnForE; 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) = Aand (A − A) ∪ (A − A) = A * A = Φ).

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

a * b = `{(a+b, "if a+b < 6"), (a + b - 6, if a +b >= 6):}`

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.

Let A = {−1, 0, 1, 2}, B = {−4, −2, 0, 2} and f, g: A → B be functions defined by f(x) = x² − x, x ∈ A and g(x) = `2|x - 1/2|- 1, x in A`. Are f and g equal?

Justify your answer. (Hint: One may note that two function f: A → B and g: A → B such that f(a) = g(a) &mn For E;a ∈A, are called equal functions).

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 f: R → R be the Signum Function defined as

f(x) = `{(1,x>0), (0, x =0),(-1, x< 0):}`

and g: R → 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 and gof coincide in (0, 1]?

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

(A) 10

(B) 16

(C) 20

(D) 8