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All questions of Relations & Functions for Year 10 Exam

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If f(x) = x2 and g(x) = cosx, which of the following is true?
  • a)
    f + g is even function
  • b)
    f – g is an odd function
  • c)
    f + g is not defined
  • d)
    f + g is an odd function
Correct answer is option 'A'. Can you explain this answer?

Raghav Bansal answered
if f(x) is an odd function
So, f(−x)=−f(x)
F(−x)=cos(f(−x))
=cos(−f(x))
=cos(f(x))
=F(x)
So cos(f(x)) is an even function
So, f(x) and g(x) is an even function

If A = {1, 2, 3}, and B = {3, 6} then the number of relations from A to B is
  • a)
    32
  • b)
    23
  • c)
    23
  • d)
    26
Correct answer is option 'D'. Can you explain this answer?

Preeti Iyer answered
The number of relations between sets can be calculated using 2mn where m and n represent the number of members in each set.
So, number of relations from A to B is 26.

Which of the following relations is not a function?
  • a)
    R= {(1,2), (3,4),(2,1),(5,1)}
  • b)
    R={(1,2), (1,4)(3,1),(5,1)}
  • c)
    R= {(1,2), (3,4)(2,1),(5,2)}
  • d)
    R= {(2,1), (4,4)(3,1),(5,1)}
Correct answer is option 'B'. Can you explain this answer?

Gaurav Kumar answered
A function is a relation in which no two ordered pairs have the same first element. A function associates each element in its domain with one and only one element in its range. R={(1,2), (1,4)(3,1),(5,1)} is not  a function because all the first elements are not different.

 If X = {1, 2, 3, 4}, Y = {1, 2, 3,…., 20}, and f: X –> Y be the correspondence which assigns each element in X the value equal to its square, then the domain, co-domain and range of f is
  • a)
    Domain = {1, 2, …, 20}, Range = {1, 2, 3, 4}, Co domain = {1, 2, 3, 4}
  • b)
    Domain = {1, 4, 9, 16}, Range = {1, 2, 3, 4}, Co domain = {1, 2, 3, …, 16}
  • c)
    Domain = {1, 2, 3, 4}, Range = {1, 4, 9, 16}, Co domain = {1, 2, 3, …, 20}
  • d)
    Domain = {1, 2, 3, 4}, Range = {1, 4, 9, 16}, Co domain = {1, 2, 3, …, 16}
Correct answer is option 'B'. Can you explain this answer?

Raghav Bansal answered
The correct option is B
Since the function is defined from 
XY.So the domain will be the set X which is {1,2,3,4}. Codomain is  what may possibly come out of a function. So codomain is the whole set Y which is {1,2,3,...,20}. Range is The range is the set of possible output values which will be the values in the set of Y which have a pre-image. That is, the value of squares. So the range is {1,4,,9,16}. 

Which of the following is not an example of polynomial function ?
  • a)
    g(x) = 8x2 + 5x – 2
  • b)
    p(x) =5x3 + 3x2 + x – 2
  • c)
    h(x) =3 root of x minus 1 over x
  • d)
    f(x) = 3x2 + x – 2
Correct answer is option 'C'. Can you explain this answer?

Lavanya Menon answered
A polynomial function is a function which involves only non-negative integer powers or only positive integer exponents of a variable in an equation.
In option C, powers of x are negative and fractional.

Let R be a relation defined as
R = {(x, y): y = 2x, x is natural number < 5} then Range of R is given as ,
  • a)
    {2, 4, 6, 8}
  • b)
    {2, 4, 6, 8, 10}
  • c)
    {1, 2, 3, 4}
  • d)
    N
Correct answer is option 'A'. Can you explain this answer?

Gaurav Kumar answered
X is a natural number and x < 5, the number is 1, 2, 3, 4
y = 2x
► x(1), y = 2 × 1 = 2
► x(2), y = 2 × 2 = 4
► x(3), y = 2 × 3 = 6
► x(4), y = 2 × 4 = 8
Range = {2, 4, 6, 8}

Number of subsets of a set of order three is
  • a)
    2
  • b)
    4
  • c)
    6
  • d)
    8
Correct answer is option 'D'. Can you explain this answer?

Raj Ghoshal answered
Number of Subsets of a Set of Order Three

To find the number of subsets of a set of order three, we need to consider all possible combinations of elements in the set.

Let's say we have a set S = {a, b, c}. We can represent each element of the set as a binary digit, where 0 represents the absence of the element and 1 represents the presence of the element.

- Empty Set: The empty set is a subset of every set, so it is included.
- Single Element Subsets: There are three single element subsets - {a}, {b}, and {c}.
- Two Element Subsets: There are three possible two-element subsets - {a, b}, {a, c}, and {b, c}.
- Three Element Subset: There is only one three-element subset - {a, b, c}.

Therefore, the total number of subsets of the set S = {a, b, c} is 1 (empty set) + 3 (single element subsets) + 3 (two-element subsets) + 1 (three-element subset) = 8.

Hence, the correct answer is option 'D' - 8.

In summary, to find the number of subsets of a set of order three, we consider all possible combinations of elements, including the empty set and subsets of different sizes. By applying this approach to the given set S = {a, b, c}, we find that there are 8 subsets in total.

Which of the following is incorrect?
  • a)
    Modulus function, Domain: R; Range: [0, infinity)
  • b)
    Signum function, Domain: R; Range: {-1, 0,1}
  • c)
    Constant function, Domain: R; Range: R
  • d)
    Identity function, Domain: R; Range: R
Correct answer is option 'C'. Can you explain this answer?

Preeti Khanna answered
Constant Function is defined as the real valued function.
f : R→R, y = f(x) = c for each x∈R and c is a constant.
So, this function basically associate each real number to a constant value.
It is a linear function where f(x1) = f(x2) for all x1,x2 ∈ R
For f : R→R, y = f(x) = c for each x ∈ R
Domain = R
Range = {c}
The value of c can be any real number.

 If f(x) = x2 – x + 1; g(x) = 7x – 3, be two real functions then (f + g)(3) is
  • a)
    25
  • b)
    3
  • c)
    7
  • d)
    18
Correct answer is option 'A'. Can you explain this answer?

Riya Banerjee answered
 f(x) = x2 – x + 1; g(x) = 7x – 3
(f+g)(x) = (x2 - x + 1 + 7x - 3)
=(x2 - x + 7x + 1 - 3)
= x2 + 6x - 2
(f+g)(3) = x2 + 6x - 2
= (3)2 + 6(3) - 2
= 9 + 18 - 2
= 25

The domain of the function f(x)=   is all real x such that
  • a)
    x<2
  • b)
    -2
  • c)
    -2 ≤ x ≤ 2
  • d)
    x>-2
Correct answer is option 'C'. Can you explain this answer?

Geetika Shah answered
4 - x2 = 0
=> (2+x)(2-x) = 0
x = +-2
Now select a test point, let it be x = 0. Then y = (4 - (0)2)1/2 = 2, so the function is defined on [-2,2]
Thus, the graph of y = (4 - x2)1/2 is a semicircle with radius 2 and domain is [-2,2]

A relation R defined on the set A = {1,2,3,5} as {(x, y): x+y >10: x,y ∈ A} is
  • a)
    Empty relation
  • b)
    Universal relation
  • c)
    Zero relation
  • d)
    Identity relation
Correct answer is option 'A'. Can you explain this answer?

Gayatri Kumar answered
This relation R is not transitive.

To show this, we need to find a counterexample where the relation fails to hold for three elements in A.

Let's consider (1,2), (2,5), and (1,5). We know that (1,2) and (2,5) are in R, since 1 is less than 2 and 2 is less than 5. Similarly, (2,5) is in R because 2 is less than 5.

However, (1,5) is not in R since 1 is less than 5. Therefore, we have a counterexample where (1,2) and (2,5) are in R, but (1,5) is not. This shows that R is not transitive.

f(x) = x is called
  • a)
    an identity function
  • b)
    a constant function
  • c)
    inverse function
  • d)
    step function
Correct answer is option 'A'. Can you explain this answer?

Mira Sharma answered
In mathematics, an identity function, also called an identity relation or identity map or identity transformation, is a function that always returns the same value that was used as its argument. In equations, the function is given by f(x) = x.

Which of the relations is not a function?
  • a)
    one many
  • b)
    domain = codomain
  • c)
    many one
  • d)
    one-one
Correct answer is option 'A'. Can you explain this answer?

Rohan Singh answered
One-to-one and many-to-one functions. A function is said to be one-to-one if every y value has exactly one x value mapped onto it, and many-to-one if there are y values that have more than one x value mapped onto them. This graph shows a many-to-one function.

Find the domain of the function f(x) = 
  • a)
    R – {-4}
  • b)
    R
  • c)
    R – {4}
  • d)
    R+
Correct answer is option 'C'. Can you explain this answer?

Lavanya Menon answered
 f(x) = 3x/2x-8
denominator can't be zero so
2x - 8 not equal to 0
x should not equal to 4
we have domain R - {4}

If n(A) = 2, n(B) = 2. What is the total number of relations from A to B?
  • a)
    4
  • b)
    32
  • c)
    12
  • d)
    16
Correct answer is option 'D'. Can you explain this answer?

Varun Kapoor answered
Hint: To solve this problem you don’t need to count the number of relations by assuming it on your own. Use the formula of the number of relations from set A to set B. 

Complete step-by-step answer:
 It is given that A = {1, 2} and B = {3, 4}
The number of elements in A is n(A)=2 and that of B is n(B) = 2.
The formula for the number of relations from one set to another is:
2(number of elements in the first set) x (number of elements of the second set) 
Therefore, we can write it as follows.
No. of relations from set A to set B = 2n(A)n(B) =  2(2*2) = 16 
Hence, the number of relations from A to B is 16.

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