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NDA II 2024 Mathematics Test - 2
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NDA II 2024 Mathematics Test - 2
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  • Question 1/10
    2.5 / -0.83

    Solutions

    Comparing above two equation

    Now,

  • Question 2/10
    2.5 / -0.83

    What is the least possible degree of polynomial with real coefficient having 2ω2, 3 + 4ω, 3 + 4ω2, 5 - ω - ω2 as roots

    Solutions

    First of all, we should not think that because of the 4 roots, the degree of the polynomial will be 4.

    We need to remember that complex roots always occur in pairs.

    Now,

    Now, to find the value of the given pair roots,

    1) 2ω2 = -1 - √3 i

    ∴ -1 + √3i will also be a root.

    2) 3 + 4ω = 3 - 2 + 2√3i

    = 1 + 2√3i

    ∴ 1 - 2√3i will also be a root.

    3) 3 + 4ω2 = 3 - 2 - 2√3i

    = 1 - 2√3i

    i.e, 3 + 4ω and 3 + 4ω2 are conjugate pairs.

    i.e. 6 is a root.

    Total we have 5 roots.

    The minimum degree of the polynomial is 5.

  • Question 3/10
    2.5 / -0.83

    The solutions of the equation z2 + |z| = 0 are:

    where, z = x + iy

    Solutions

    now,

    i) if x ≥ 0

    x2 + x = 0

    x(x + 1) = 0

    x = 0, x = -1

    ∴ x = 0 (∵ x ≥ 0)

    y = 0, x = 0 is solution.

    ii) if x < 0

    x2 - x = 0

    x(x - 1) = 0

    ∴ x = 0, x = 1

    Both are not possible

    Case: 2

    x = 0

    -y2 + |y| = 0

    now,

    i) if y ≥ 0

    -y2 + y = 0

    y(1 - y) = 0

    y = 0, y = 1

    Two solutions:

    (a) x = 0, y = 0 is a solution (z = 0)

    (b) x = 0, y = 1 is a solution (z = i)

    ii) if y < 0

    -y2 - y = 0

    -y(1 + y) = 0

    y = 0, y = -1

    Two solutions:

    (a) x = 0, y = 0 is a solution (z = 0)

    (b) x = 0, y = -1 is a solution (z = -i)

  • Question 4/10
    2.5 / -0.83

    If ω is an imaginary cube root of unity, then value of

    Solutions

    Concept:

    If 1, ω, ω2 are the cube roots of unity,

    ⇒ 1 - ω2 + 1 - ω

    ⇒ 2 - (ω2 + ω)

    ⇒ 2 - (-1)       (∵ 1 + ω + ω2 = 0)

    ⇒ 2 + 1

    ⇒ 3

  • Question 5/10
    2.5 / -0.83

    Convert 45 into binary number.

    Solutions

    Concept:

    Convert decimal to binary

    Conversion steps:

    • Divide the number by 2.
    • Get the integer quotient for the next iteration.
    • Get the remainder for the binary digit.
    • Repeat the steps until the quotient is equal to 0.

    Calculation:

    Here, we have to find the binary equivalent of 45

    So, the binary equivalent of 45 is 101101

    ∴ (45)10 = (101101)2

  • Question 6/10
    2.5 / -0.83

    If 5th term of an Arithmetic progression (AP) series is 16 and 9th term is 22, then find the seventh (7th) term of the series.

    Solutions

    Concept used:

    The middle position of an AP series is the average of the series,

    Example: 1, 2, 3, 4, 5 are in AP, the average of the AP = (1 + 5)/2 = 3 is the middle position

    Calculation:

    Here 7th term is the middle position of 5th term and 9th term then the 7th term = (16 + 22)/2 = 19

    ∴ The correct answer is 19

  • Question 7/10
    2.5 / -0.83

    If a1, a2, ..., a8 are eight numbers whose  average is 40, and average of numbers at even places is 25, then average of numbers at odd places is:

    Solutions

    Given:

    a1, a2, ..., a8 are eight numbers whose  average = 40

    Average of numbers at even places = 25

    Formula used:

    Average = (Sum of terms)/(Number of terms)

    Calculation:

    The sum of these eight numbers = 8 × 40 = 320

    The average of the numbers at even places (a2, a4, a6, a8) = 25.

    The sum of these four numbers = 4 × 25 = 100

    Now, we subtract the sum of the numbers at even places from the total sum, and then divide by the number of odd places.

    The sum of the numbers at odd places = 320 - 100 = 220

    There are 4 numbers at odd places, their average is 220/4 = 55

    ∴ Average of numbers at odd places is 55.

  • Question 8/10
    2.5 / -0.83

    Solutions

    comparing 1) and (2), we get

    Hence, x = 1

  • Question 9/10
    2.5 / -0.83

    If the roots of a(b - c) x+ b(c - a) x + c(a - b) = 0 are equal, then a, b, c are:

    Solutions

    Concept used:

    Euation Ax+ Bx + C = 0

    If roots are equal B2 - 4AC = 0

    Formula Used:

    (x - y)2 = x2 - 2xy + y2

    (x + y + z)2 = x2 + y2 + z2 + 2xy + 2yz + 2zx

    Calculation:

    a(b - c) x2 + b(c - a) x + c(a - b) = 0

    Where A = a(b - c) , B = b(c - a) & C =  c(a - b)

    Now, 

    ⇒ [b(c - a)]2 - 4 × a(b - c) × c(a - b) = 0 

    ⇒ b2(c+ a- 2ac) - 4ac(ab - b2 -ac + bc) = 0

    ⇒ b2c+ b2a2 - 2acb2 - 4a2bc + 4acb2 + 4a2c2 - 4abc2 = 0

    ⇒ a2b2 + b2c2 + 4a2c2 + 2acb2 - 4a2bc - 4abc2  = 0

    By using the above identiy

    ⇒ (ab + bc - 2ac)2 = 0

    ⇒ ab + bc - 2ac = 0 

    ⇒ b(a + c) = 2ac 

    ⇒ b = 2ac/(a + c)

    So, a, b & c are in harmonic progression.

    ∴ The correct answer is Harmonic progression.

  • Question 10/10
    2.5 / -0.83

    Solutions

    Formula used:

    The formula used for summation for G.P: (r < 1 and series is of infinite terms)

    Where, 

    S, is the summation of G.P

    a, is the first term

    r, is the common ratio

    Calculation:

    Let S be the sum of the given series.

    The required series can be written as:

    Now, the above series becomes Geometric series with a common ratio of 10/20

    Additional Information

    (1) The formula used for summation for G.P: (r < 1 and series is of finite terms)

    Where,

    S = the summation of G.P

    a = the first term

    r = the common ratio

    n = the number of terms

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