FUNCTION Trigonometry MCQ Quiz for LT TGT/PGT Maths Practice Test with Timer

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Trigonometry MCQ Quiz for TGT/PGT Maths Practice Test with Timer


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Complete Mathematics Questions and Answers

Comprehensive Q&A Collection

31. If f(x) = x – [x], where [x] is the greatest integer less than or equal to x, then f(-1/2) is equal to:

  • (a) -1
  • (b) -1/2
  • (c) 0
  • (d) 1/2

Correct Answer: (d) 1/2

Explanation:

The function f(x) = x – [x] represents the fractional part of x.

We need to find f(-1/2). First, we find the value of [-1/2].

The greatest integer less than or equal to -0.5 is -1. So, [-1/2] = -1.

Now, substitute this value into the function:

f(-1/2) = -1/2 – [-1/2] = -1/2 – (-1) = -1/2 + 1 = 1/2.

S.C.R.A. 2000


33. The domain of f(x) = 1 / √(|x| – x) is:

  • (a) (-∞, 0)
  • (b) (-∞, 0]
  • (c) (0, ∞)
  • (d) [0, ∞)

Correct Answer: (a) (-∞, 0)

Explanation:

For the function to be defined, the expression inside the square root must be strictly positive (since it’s in the denominator).

So, |x| – x > 0, which means |x| > x.

We analyze this condition in two cases:

  1. If x ≥ 0, then |x| = x. The inequality becomes x > x, which is false for all x.
  2. If x < 0, then |x| = -x. The inequality becomes -x > x. Adding x to both sides gives 0 > 2x, or x < 0.

The condition |x| > x is only true when x is a negative number. Therefore, the domain is x < 0, or (-∞, 0).

Raj. (P.E.T.) 2000; Kerala (C.E.E.) 1989


39. The function sin(x/3) is periodic with period:

  • (a) 2π
  • (b) 6π
  • (c) 4π
  • (d) 8π

Correct Answer: (b) 6π

Explanation:

The period of the standard sine function, sin(x), is 2π. For a function of the form f(x) = sin(bx), the period is given by the formula T = 2π / |b|.

In this case, the function is sin(x/3), so b = 1/3.

Therefore, the period T = 2π / (1/3) = 2π * 3 = 6π.

Pb. (C.E.T.) 1999


47. If f(x) = cos(log x), then f(x)f(y) – 1/2[f(x/y) + f(xy)] has the value:

  • (a) -1
  • (b) 1/2
  • (c) -2
  • (d) 0

Correct Answer: (d) 0

Explanation:

We are given f(x) = cos(log x). Let’s evaluate each term in the expression.

  • f(x)f(y) = cos(log x)cos(log y)
  • f(x/y) = cos(log(x/y)) = cos(log x – log y)
  • f(xy) = cos(log(xy)) = cos(log x + log y)

Now substitute these into the main expression:

Expression = cos(log x)cos(log y) – 1/2[cos(log x – log y) + cos(log x + log y)]

We use the trigonometric identity: cos(A – B) + cos(A + B) = 2cosAcosB.

Let A = log x and B = log y. Then the expression in the bracket becomes:

[cos(log x – log y) + cos(log x + log y)] = 2cos(log x)cos(log y).

Substituting this back:

Expression = cos(log x)cos(log y) – 1/2[2cos(log x)cos(log y)]

Expression = cos(log x)cos(log y) – cos(log x)cos(log y) = 0.

Karnataka (C.E.T.) 1999; Kerala C.E.E. 2001


52. Let f(x) = 4x / (4x + 2). Then f(x) + f(1 – x) is equal to:

  • (a) 0
  • (b) 1
  • (c) -1
  • (d) none of these

Correct Answer: (b) 1

Explanation:

We are given the function f(x) = 4x / (4x + 2).

First, let’s find the expression for f(1 – x):

f(1 – x) = 4(1-x) / (4(1-x) + 2) = (4/4x) / ((4/4x) + 2)

To simplify, multiply the numerator and denominator by 4x:

f(1 – x) = (4) / (4 + 2 * 4x) = 4 / (2(2 + 4x)) = 2 / (4x + 2)

Now, let’s add f(x) and f(1 – x):

f(x) + f(1 – x) = [4x / (4x + 2)] + [2 / (4x + 2)]

Since they have a common denominator, we can add the numerators:

f(x) + f(1 – x) = (4x + 2) / (4x + 2) = 1.

Roorkee 1998


61. If f(x) = (a – xn)1/n, then f(f(x)) equals:

  • (a) x
  • (b) a – x
  • (c) xn
  • (d) x1/n

Correct Answer: (a) x

Explanation:

To find f(f(x)), we substitute the expression for f(x) into the function itself.

f(f(x)) = f( (a – xn)1/n )

Now, replace ‘x’ in the original function definition with ‘(a – xn)1/n‘:

f(f(x)) = [a – { (a – xn)1/n }n ]1/n

The powers 1/n and n cancel each other out:

f(f(x)) = [a – (a – xn)]1/n

Simplify the expression inside the brackets:

f(f(x)) = [a – a + xn]1/n = [xn]1/n

Again, the powers n and 1/n cancel out, leaving:

f(f(x)) = x.

C.E.T. 1997; Roorkee 1997


69. The minimum value of sin6x + cos6x is:

  • (a) 1/4
  • (b) 0
  • (c) 1
  • (d) none of these

Correct Answer: (a) 1/4

Explanation:

We can simplify the expression f(x) = sin6x + cos6x.

  1. Rewrite using a3 + b3 identity, where a = sin2x and b = cos2x: f(x) = (sin2x)3 + (cos2x)3
  2. Using a3 + b3 = (a + b)3 – 3ab(a + b): f(x) = (sin2x + cos2x)3 – 3(sin2x)(cos2x)(sin2x + cos2x)
  3. Since sin2x + cos2x = 1: f(x) = (1)3 – 3sin2x cos2x(1) = 1 – 3sin2x cos2x
  4. Use the double angle identity sin(2x) = 2sinxcosx, so sin2x cos2x = (1/4)sin2(2x): f(x) = 1 – 3 * (1/4)sin2(2x) = 1 – (3/4)sin2(2x)
  5. To find the minimum value of f(x), we must subtract the maximum possible value of (3/4)sin2(2x). The maximum value of sin2(2x) is 1. Minimum value of f(x) = 1 – (3/4) * 1 = 1/4.

I.I.T. 1992; C.E.T. 1996


82. If f(x) is an odd periodic function with period 2, then f(4) equals:

  • (a) 0
  • (b) 2
  • (c) 4
  • (d) -4

Correct Answer: (a) 0

Explanation:

  1. Periodicity: The function has a period of 2. This means f(x + 2) = f(x) for all x. We can use this to relate f(4) to f(0): f(4) = f(2 + 2) = f(2) = f(0 + 2) = f(0). So, f(4) = f(0).
  2. Odd Function Property: The function is odd. This means f(-x) = -f(x) for all x. Let’s apply this property for x = 0: f(-0) = -f(0) f(0) = -f(0) 2f(0) = 0 f(0) = 0.
  3. Conclusion: Since f(4) = f(0) and f(0) = 0, it follows that f(4) = 0.

I.I.T. 1998


87. If the function f(x) = cos2x + cos2(π/3 + x) + cos2(π/3 – x) is constant, then the value of this constant is:

  • (a) 0
  • (b) 3/4
  • (c) 1
  • (d) 4/3

Correct Answer: There appears to be a typo in the options. The correct answer is 3/2.

Explanation:

  1. Use the identity cos2θ = (1 + cos(2θ))/2.
    f(x) = (1 + cos(2x))/2 + (1 + cos(2(π/3 + x)))/2 + (1 + cos(2(π/3 – x)))/2
  2. Combine terms:
    f(x) = 3/2 + 1/2 [cos(2x) + cos(2π/3 + 2x) + cos(2π/3 – 2x)]
  3. Use the identity cos(A + B) + cos(A – B) = 2cosAcosB. Let A = 2π/3 and B = 2x.
    cos(2π/3 + 2x) + cos(2π/3 – 2x) = 2cos(2π/3)cos(2x)
  4. We know cos(2π/3) = -1/2.
    So, 2(-1/2)cos(2x) = -cos(2x).
  5. Substitute this back into the expression for f(x):
    f(x) = 3/2 + 1/2 [cos(2x) – cos(2x)] = 3/2 + 1/2 [0] = 3/2.

The function is constant with a value of 3/2. Since this is not an option, there might be a typo in the question or options provided.

Roorkee 1991


95. sin-1(cos(sin-1x)) + cos-1(sin(cos-1x)) is equal to:

  • (a) 0
  • (b) π/4
  • (c) π/2
  • (d) 3π/4

Correct Answer: (c) π/2

Explanation:

Let’s simplify each term separately.

  1. First term: sin-1(cos(sin-1x))
    Let sin-1x = θ, so x = sinθ.
    We need sin-1(cosθ). We know cosθ = sin(π/2 – θ).
    So, sin-1(cosθ) = sin-1(sin(π/2 – θ)) = π/2 – θ = π/2 – sin-1x.
  2. Second term: cos-1(sin(cos-1x))
    Let cos-1x = φ, so x = cosφ.
    We need cos-1(sinφ). We know sinφ = cos(π/2 – φ).
    So, cos-1(sinφ) = cos-1(cos(π/2 – φ)) = π/2 – φ = π/2 – cos-1x.
  3. Adding the terms:
    Expression = (π/2 – sin-1x) + (π/2 – cos-1x)
    = π – (sin-1x + cos-1x)
  4. Using the identity sin-1x + cos-1x = π/2:
    Expression = π – (π/2) = π/2.

Pb. (C.E.T.) 1990


101. If f(x) = (3x + 2) / (5x – 3), then:

  • (a) f-1(x) = f(x)
  • (b) f-1(x) = -f(x)
  • (c) f-1(f(x)) = -x
  • (d) f-1(x) = 1/19 f(x)

Correct Answer: (a) f-1(x) = f(x)

Explanation:

To find the inverse function f-1(x), we follow these steps:

  1. Let y = f(x). So, y = (3x + 2) / (5x – 3).
  2. Swap x and y to start finding the inverse: x = (3y + 2) / (5y – 3).
  3. Solve for y:
    x(5y – 3) = 3y + 2
    5xy – 3x = 3y + 2
    5xy – 3y = 3x + 2
    y(5x – 3) = 3x + 2
    y = (3x + 2) / (5x – 3).
  4. So, f-1(x) = (3x + 2) / (5x – 3).

Comparing f-1(x) with the original function f(x), we see that they are identical. Thus, f-1(x) = f(x).

Pb. (C.E.T.) 1989


108. The domain of the function f(x) = sin-1(x – 3) / √(9 – x2) is:

  • (a) [1, 2]
  • (b) (2, 3)
  • (c) [2, 3)
  • (d) [1, 2)

Correct Answer: (c) [2, 3)

Explanation:

We must satisfy the conditions for both the numerator and the denominator.

  1. Numerator: sin-1(x – 3)
    The argument of arcsin must be in [-1, 1].
    -1 ≤ x – 3 ≤ 1
    2 ≤ x ≤ 4. So, the interval is [2, 4].
  2. Denominator: √(9 – x2)
    The expression inside the square root must be strictly positive.
    9 – x2 > 0
    x2 < 9
    -3 < x < 3. So, the interval is (-3, 3).
  3. Intersection: We need to find the intersection of [2, 4] and (-3, 3).
    The common values are those that are greater than or equal to 2 AND less than 3.
    Therefore, the domain is [2, 3).

A.I.E.E.E. 2004


111. The function f satisfies the functional equation 3f(x) + 2f((x + 59)/(x – 1)) = 10x + 30 for all x ≠ 1. The value of f(7) is:

  • (a) 8
  • (b) 4
  • (c) -8
  • (d) 11

Correct Answer: (b) 4

Explanation:

This is a system of equations problem in disguise.

  1. Let x = 7:
    3f(7) + 2f((7 + 59)/(7 – 1)) = 10(7) + 30
    3f(7) + 2f(66/6) = 70 + 30
    3f(7) + 2f(11) = 100 —(Eq. 1)
  2. Let x = 11: Notice that if we substitute x=11, the term (x+59)/(x-1) becomes (11+59)/(11-1) = 70/10 = 7. This will give us a second equation with f(7) and f(11).
    3f(11) + 2f((11 + 59)/(11 – 1)) = 10(11) + 30
    3f(11) + 2f(7) = 110 + 30
    2f(7) + 3f(11) = 140 —(Eq. 2)
  3. Solve the system:
    Multiply Eq. 1 by 3: 9f(7) + 6f(11) = 300
    Multiply Eq. 2 by 2: 4f(7) + 6f(11) = 280
    Subtract the new second equation from the new first one:
    (9f(7) – 4f(7)) = 300 – 280
    5f(7) = 20
    f(7) = 4.

Kerala (P.E.T.) 2005


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