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NDA 2025
Exam
NDA
Year
2025
Subject
Mathematics
Chapter
Complex Number

NDA 2025 · Mathematics · Complex Number

If α = -1 + -3 2 , then what is the value of (1 + α^ 19 - α^ 35 )^...

If α=−1+−32\alpha = \dfrac{-1 + \sqrt{-3}}{2}, then what is the value of (1+α19−α35)100−(1−3α25+α38)50(1 + \alpha^{19} - \alpha^{35})^{100} - (1 - 3\alpha^{25} + \alpha^{38})^{50}?

Options

  1. A−2-2
  2. B−1-1
  3. C00
  4. D22

Correct answer

C. 00

Step-by-step solution

Given α=−1+−32\alpha = \dfrac{-1 + \sqrt{-3}}{2}, which is the complex cube root of unity, ω\omega.

We know that ω3=1\omega^3 = 1 and 1+ω+ω2=01 + \omega + \omega^2 = 0.

Substituting α=ω\alpha = \omega into the given expression, we simplify the powers of ω\omega:

α19=ω19=(ω3)6⋅ω=ω\alpha^{19} = \omega^{19} = (\omega^3)^6 \cdot \omega = \omega

α35=ω35=(ω3)11⋅ω2=ω2\alpha^{35} = \omega^{35} = (\omega^3)^{11} \cdot \omega^2 = \omega^2

α25=ω25=(ω3)8⋅ω=ω\alpha^{25} = \omega^{25} = (\omega^3)^8 \cdot \omega = \omega

α38=ω38=(ω3)12⋅ω2=ω2\alpha^{38} = \omega^{38} = (\omega^3)^{12} \cdot \omega^2 = \omega^2

The first term becomes:

(1+α19−α35)100=(1+ω−ω2)100(1 + \alpha^{19} - \alpha^{35})^{100} = (1 + \omega - \omega^2)^{100}

Since 1+ω=−ω21 + \omega = -\omega^2, this reduces to:

(−ω2−ω2)100=(−2ω2)100=2100ω200(-\omega^2 - \omega^2)^{100} = (-2\omega^2)^{100} = 2^{100} \omega^{200}

Since 200=3×66+2200 = 3 \times 66 + 2, ω200=ω2\omega^{200} = \omega^2. Thus, the first term is 2100ω22^{100} \omega^2.

The second term becomes:

(1−3α25+α38)50=(1−3ω+ω2)50(1 - 3\alpha^{25} + \alpha^{38})^{50} = (1 - 3\omega + \omega^2)^{50}

Since 1+ω2=−ω1 + \omega^2 = -\omega, this reduces to:

(−ω−3ω)50=(−4ω)50=450ω50=(22)50ω50=2100ω50(-\omega - 3\omega)^{50} = (-4\omega)^{50} = 4^{50} \omega^{50} = (2^2)^{50} \omega^{50} = 2^{100} \omega^{50}

Since 50=3×16+250 = 3 \times 16 + 2, ω50=ω2\omega^{50} = \omega^2. Thus, the second term is 2100ω22^{100} \omega^2.

Subtracting the second term from the first term:

2100ω2−2100ω2=02^{100} \omega^2 - 2^{100} \omega^2 = 0

Answer: 00
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