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Question 201

National Defence Academy (NDA) 2025• Mathematics

Consider the following for the two (02) items that follow:

Let the function y = (1 - cos x)-1 wherex≠2nπx \ne 2n\pi and n is an integer

What is the range of the function?

  1. AOption (a)

    [0,∞)

  2. BOption (b)

    [0.5,∞)

  3. COption (c)

    [1,∞)

  4. DOption (d)

    (−∞,0.5]

View answer & explanation

Correct answer

Answer: (b)B.

[0.5,∞)

Why this answer is correct

Calculation:

Given,

The function isy=(1−cos⁡(x))−1y = \left( 1 - \cos(x) \right)^{-1} , where x≠2nπx \neq 2n\pi and n  is an integer.

The cosine function has a range of  [-1, 1] , so cos(x) can take values from ( -1) to ( 1 ).

The expression 1−cos⁡(x)1 - \cos(x) will take values from:

1−1=0to1−(−1)=2 1 - 1 = 0 \quad \text{to} \quad 1 - (-1) = 2

So, (1 - cos(x)) takes values in the range (0,2](0, 2] , but x≠2nπx \neq 2n\pi excludes the value 0.

Since y=11−cos⁡(x)y = \frac{1}{1 - \cos(x)} , the reciprocal function will take values in the range [12,∞)\left[ \frac{1}{2}, \infty \right)

∴ The range of the function is [0.5,∞)[0.5, \infty) .

The correct answer is Option (b)

Question 202

National Defence Academy (NDA) 2025• Mathematics

Consider the following for the two (02) items that follow:

Let the function y = (1 - cos x)-1 wherex≠2nπx \ne 2n\pi and n is an integer

What is ∫ydx equal to? 

where c is the constant of integration.

  1. AOption (a)

    −tan(x/2)+c

  2. BOption (b)

    −cot(x/2)+c

  3. COption (c)

    tan(x/2)+c

  4. DOption (d)

    cot(x/2)+c

View answer & explanation

Correct answer

Answer: (b)B.

−cot(x/2)+c

Why this answer is correct

Calculation:

Given,

The function is y=(1−cos⁡(x))−1y = \left(1 - \cos(x)\right)^{-1} , wherex≠2nπx \neq 2n\pi and n is an integer.

The given function can be written as:

y=11−cos⁡(x) y = \frac{1}{1 - \cos(x)}

Using the identity 1−cos⁡(x)=2sin⁡2(x2)1 - \cos(x) = 2\sin^2\left(\frac{x}{2}\right) , we rewrite the function as:

y=12sin⁡2(x2) y = \frac{1}{2\sin^2\left(\frac{x}{2}\right)}

The integral we need to evaluate is:

∫dx2sin⁡2(x2) \int \frac{dx}{2\sin^2\left(\frac{x}{2}\right)}

12∫csc⁡2(x2)dx \frac{1}{2} \int \csc^2\left(\frac{x}{2}\right) dx

The integral of csc⁡2(x)\csc^2(x) is known to be −cot⁡(x) -\cot(x) , so we get:

12(−cot⁡(x2))+C \frac{1}{2} \left( -\cot\left(\frac{x}{2}\right) \right) + C

−12cot⁡(x2)+C -\frac{1}{2} \cot\left(\frac{x}{2}\right) + C

The final result is −cot⁡(x2)+C -\cot\left(\frac{x}{2}\right) + C

Hence, the correct answer is Option 2.

Question 203

National Defence Academy (NDA) 2025• Mathematics

Consider the following for the two (02) items that follow: Let the function f(x)=sin[x], where [⋅] is the greatest integer function and g(x)=∣x∣.

What lim⁡x→0f(x)g(x)\lim_{x \to 0} {f(x) g(x)} is  equal to?

  1. AOption (a)

    -1

  2. BOption (b)

    0

  3. COption (c)

    1

  4. DOption (d)

    Limit does not exist

View answer & explanation

Correct answer

Answer: (b)B.

0

Why this answer is correct

Calculation:

Given,

The function isf(x)=sin⁡(⌊x⌋)f(x) = \sin(\lfloor x \rfloor) , where⌊x⌋\lfloor x \rfloor is the greatest integer function, and g(x) = |x| , the absolute value function.

We are tasked with finding:

lim⁡x→0f(x)g(x) \lim_{x \to 0} f(x) g(x)

For g(x)=∣x∣g(x) = |x| , we know that:

lim⁡x→0g(x)=0 \lim_{x \to 0} g(x) = 0

For f(x)=sin⁡(⌊x⌋)f(x) = \sin(\lfloor x \rfloor) , we know that:

For x→0+x \to 0^+ ), ⌊x⌋=0 \lfloor x \rfloor = 0 , so f(x) = sin(0) = 0 .

For x→0− x \to 0^- , ⌊x⌋=−1 \lfloor x \rfloor = -1 , so f(x)=sin⁡(−1)f(x) = \sin(-1) , which is a nonzero constant.

Evaluating the limit:

Forx→0+x \to 0^+ ,f(x)g(x)=0×x=0f(x)g(x) = 0 \times x = 0

Forx→0−x \to 0^- , f(x)g(x)=sin⁡(−1)×(−x)f(x)g(x) = \sin(-1) \times (-x) , which approaches 0 as x→0−.x \to 0^- ..

∴ The value of lim⁡x→0f(x)g(x)\lim_{x \to 0} f(x) g(x) is 0.

The correct answer is Option (2).

Question 204

National Defence Academy (NDA) 2025• Mathematics

Consider the following for the two (02) items that follow: Let the function f(x)=sin[x], where [⋅] is the greatest integer function and g(x)=∣x∣.

What is lim⁡x→0f(x)g(x)\lim_{x \to 0} \frac{f(x)}{g(x)} equal to?

  1. AOption (a)

    −sin1

  2. BOption (b)

    sin1

  3. COption (c)

    0

  4. DOption (d)

    Limit does not exist

View answer & explanation

Correct answer

Answer: (d)D.

Limit does not exist

Why this answer is correct

Calculation:

Given,

The function is f(x)=sin⁡(⌊x⌋) f(x) = \sin(\lfloor x \rfloor) , where ⌊x⌋\lfloor x \rfloor is the greatest integer function, and g(x) = |x| , the absolute value function.

We are tasked with finding:

lim⁡x→0f(x)g(x) \lim_{x \to 0} \frac{f(x)}{g(x)}

For g(x)=∣x∣ g(x) = |x| , we know that:

lim⁡x→0g(x)=0 \lim_{x \to 0} g(x) = 0

For f(x)=sin⁡(⌊x⌋) f(x) = \sin(\lfloor x \rfloor) , we know that:

For x→0+ x \to 0^+ , ⌊x⌋=0 \lfloor x \rfloor = 0 , so f(x) = sin(0) = 0 .

For x→0− x \to 0^- , ⌊x⌋=−1 \lfloor x \rfloor = -1 , so f(x)=sin⁡(−1) f(x) = \sin(-1) , which is a nonzero constant.

Evaluating the limit:

For x→0+ x \to 0^+ , f(x)g(x)=0x=0 \frac{f(x)}{g(x)} = \frac{0}{x} = 0

For x→0− x \to 0^- , f(x)g(x)=sin⁡(−1)−x \frac{f(x)}{g(x)} = \frac{\sin(-1)}{-x} , which becomes undefined as x→0− x \to 0^- because the denominator approaches 0, but the numerator remains a nonzero constant.

∴ Since the left-hand and right-hand limits do not match, the limit does not exist.

The correct answer is Option (4):

Question 205

National Defence Academy (NDA) 2025• Mathematics

Consider the following for the two (02) items that follow:

Let the curve f(x) = |x - 3|

What is the domain of the function (f(x))?

  1. AOption (a)

    (0, ∞)

  2. BOption (b)

    (3,∞)

  3. COption (c)

    (-∞, ∞)

  4. DOption (d)

    (-∞.∞)\3

View answer & explanation

Correct answer

Answer: (c)C.

(-∞, ∞)

Why this answer is correct

Calculation:

Given,

The function is f(x)=∣x−3∣f(x) = |x - 3| , which is an absolute value function.

The domain of an absolute value function f(x)=∣x−a∣f(x) = |x - a| is all real numbers, because the absolute value function is defined for all values of x. The function handles both positive and negative inputs for x .

Since there are no restrictions or undefined points for the absolute value function, the domain is all real numbers.

∴ The domain of the function is (−∞,∞)(-\infty, \infty)

Hence, the correct answer is Option 3.

Question 206

National Defence Academy (NDA) 2025• Mathematics

Consider the following for the two (02) items that follow:

Let the curve f(x) = |x - 3|

What is the area bounded by the curve f(x) and y = 3?

  1. AOption (a)

    3 square units

  2. BOption (b)

    4-5 square units

  3. COption (c)

    7-5 square units

  4. DOption (d)

    9 square units

View answer & explanation

Correct answer

Answer: (d)D.

9 square units

Why this answer is correct

Calculation:

Given,

The function is f(x) = |x - 3| , and we need to find the area bounded by the curve and the line y = 3.

To find the points of intersection, we set the function equal to 3:

∣x−3∣=3 |x - 3| = 3

Solving for x :

  • Forx≥3 x \geq 3 , x−3=3x - 3 = 3 , which gives x = 6 .

  • For ( x < 3 ), 3 - x = 3 , which gives x = 0 .

Therefore, the points of intersection are x = 0  and x = 6 .

The area can be calculated by integrating the difference between the curve and the line from x = 0 to x = 6. The integral is split into two parts due to the absolute value function:

A=∫03(3−x),dx+∫36(x−3),dx A = \int_{0}^{3} (3 - x) , dx + \int_{3}^{6} (x - 3) , dx

For x in [0, 3] , ( f(x) = 3 - x ), and for ( x in [3, 6] ), ( f(x) = x - 3 ).

Compute both integrals:

  • For x in [0, 3] :

∫03(3−x),dx=[3x−x22]03=9−4.5=4.5 \int_{0}^{3} (3 - x) , dx = \left[ 3x - \frac{x^2}{2} \right]_{0}^{3} = 9 - 4.5 = 4.5

  • For x in [3, 6] :

∫36(x−3),dx=[x22−3x]36=4.5 \int_{3}^{6} (x - 3) , dx = \left[ \frac{x^2}{2} - 3x \right]_{3}^{6} = 4.5

Step 4: The total area is the sum of the two areas:

A=4.5+4.5=9,square units A = 4.5 + 4.5 = 9 , \text{square units}

∴ The total area bounded by the curve and the line is 9 square units.

The correct answer is Option (4):

Question 207

National Defence Academy (NDA) 2025• Mathematics

Consider the following for the two (02) items that follow:

Let f = {(1, 1), (2, 4), (3, 7), (4, 10)}

If f(x) = px + q then what is the value of (p + q) ?

  1. AOption (a)

    -1

  2. BOption (b)

    0

  3. COption (c)

    1

  4. DOption (d)

    5

View answer & explanation

Correct answer

Answer: (c)C.

1

Why this answer is correct

Calculation:

Given,

The function is f=(1,1),(2,4),(3,7),(4,10)f = {(1, 1), (2, 4), (3, 7), (4, 10)} , and we are also given that the function is f(x)=px+q f(x) = px + q , where p and q  are constants.

Using the points f(1) = 1  and f(2) = 4 , we create the following system of equations:

  • From f(1) = 1 , we have p(1)+q=1p(1) + q = 1 , so p + q = 1 .......(1).
  • From f(2) = 4 , we have p(2) + q = 4 , so 2p + q = 4  ..........( 2).

Subtract Equation 1 from Equation 2:

(2p+q)−(p+q)=4−1 (2p + q) - (p + q) = 4 - 1

p=3 p = 3

Now, substitute p = 3 into Equation 1:

3+q=1 3 + q = 1

q=−2 q = -2

p+q=3+(−2)=1 p + q = 3 + (-2) = 1

∴ The value of p + q  is 1.

The correct answer is Option (3).

Question 208

National Defence Academy (NDA) 2025• Mathematics

Consider the following for the two (02) items that follow:

Let f = {(1, 1), (2, 4), (3, 7), (4, 10)}

Consider the following statements:

I. f is one-one function.

II. f is onto function if the codomain is the set of natural numbers.

Which of the statements given above is/are correct?

  1. AOption (a)

    I only

  2. BOption (b)

    II only

  3. COption (c)

    Both I and II

  4. DOption (d)

    Neither I not II

View answer & explanation

Correct answer

Answer: (a)A.

I only

Why this answer is correct

Calculation:

Given,

The function is f(x)=px+qf(x)=px+q, a linear polynomial.

Since f(x)=px+qf(x)=px+q is linear with p≠0p\neq0, it is one-one (injective): different xx give different f(x)f(x).

The actual outputs given are 1,4,7,10{1,4,7,10}, so the range of ff is 1,4,7,10{1,4,7,10}.

The codomain is the set of natural numbers N\mathbb{N}. For ff to be onto, its range must equal its codomain, but here:

1,4,7,10≠N{1,4,7,10}\neq\mathbb{N}

∴ f is one-one but not onto.

Hence, the correct answer is Option 1.

Question 209

National Defence Academy (NDA) 2025• Mathematics

Consider the following for the two (02) items that follow :

Let the function f(x) = x2- 1

What is lim⁡x→1f∘f(x)\lim_{x \to 1} {f \circ f(x)} equal to?

  1. AOption (a)

    -1

  2. BOption (b)

    0

  3. COption (c)

    1

  4. DOption (d)

    2

View answer & explanation

Correct answer

Answer: (a)A.

-1

Why this answer is correct

Calculation:

Given,

The function is f(x)=x2−1 f(x) = x^2 - 1 and we are tasked with finding lim⁡x→1(f∘f(x)) \lim_{x \to 1} (f \circ f(x)) .

f∘f(x)=f(f(x)) f \circ f(x) = f(f(x))

Given f(x)=x2−1 f(x) = x^2 - 1 , we substitute f(x) f(x) into itself:

f(f(x))=f(x2−1) f(f(x)) = f(x^2 - 1)

Now, apply the function f f to (x2−1) (x^2 - 1) :

f(x2−1)=(x2−1)2−1 f(x^2 - 1) = (x^2 - 1)^2 - 1

This simplifies to:

f(x2−1)=x4−2x2+1−1=x4−2x2 f(x^2 - 1) = x^4 - 2x^2 + 1 - 1 = x^4 - 2x^2

Thus, f∘f(x)=x4−2x2 f \circ f(x) = x^4 - 2x^2 .

Now, we need to find lim⁡x→1(x4−2x2) \lim_{x \to 1} (x^4 - 2x^2) .

Substitute x = 1 into the function:

f∘f(1)=14−2(12)=1−2=−1 f \circ f(1) = 1^4 - 2(1^2) = 1 - 2 = -1

∴ The value of lim⁡x→1(f∘f(x)) \lim_{x \to 1} (f \circ f(x)) is -1.

The correct answer is Option (1).

Question 210

National Defence Academy (NDA) 2025• Mathematics

Consider the following for the two (02) items that follow :

Let the function f(x) = x2- 1

What is the area bounded by the function f(x) and the x-axis?

  1. AOption (a)

    1/3 square unit

  2. BOption (b)

    2/3 square unit

  3. COption (c)

    4/3 square units

  4. DOption (d)

    2 square units

View answer & explanation

Correct answer

Answer: (c)C.

4/3 square units

Why this answer is correct

Calculation:

 

 

The function is y=x2−1 y = x^2 - 1 , and we need to find the area bounded by the curve and the x-axis between x = -1  and x = 1 .

The required area is given by the definite integral of the function from  -1  to 1 :

Area=∫−11(x2−1),dx \text{Area} = \int_{-1}^{1} (x^2 - 1) , dx

∫(x2−1),dx=x33−x \int (x^2 - 1) , dx = \frac{x^3}{3} - x

Evaluate the integral from  -1 to  1 :

[x33−x]−11=(133−1)−((−1)33−(−1)) \left[\frac{x^3}{3} - x\right]_{-1}^{1} = \left(\frac{1^3}{3} - 1\right) - \left(\frac{(-1)^3}{3} - (-1)\right)

=(13−1)−(−13+1)=(13−33)−(−13+33)=23−23=43 = \left(\frac{1}{3} - 1\right) - \left(\frac{-1}{3} + 1\right) = \left(\frac{1}{3} - \frac{3}{3}\right) - \left(\frac{-1}{3} + \frac{3}{3}\right) = \frac{2}{3} - \frac{2}{3} = \frac{4}{3}

∴ The area is 43 \frac{4}{3} square units.

Hence, the correct answer is Option 3.