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Official PYQ · 1995

GATE CS 1995 Q2.8 — Calculus: Limits, Continuity, Differentiability

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If the cube roots of unity are 1,ω1, \omega and ω2\omega^2, then the roots of the following equation are (x−1)3+8=0(x-1)^3 +8 =0

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Answer: C

We are given the equation:

(x−1)3+8=0(x-1)^3 + 8 = 0

Rearranging the terms, we get:

(x−1)3=−8(x-1)^3 = -8

Taking the cube root on both sides:

x−1=(−8)1/3x-1 = (-8)^{1/3}

Since (−8)1/3=−2×(1)1/3(-8)^{1/3} = -2 \times (1)^{1/3}, and the cube roots of unity are 1,ω, and ω21, \omega, \text{ and } \omega^2, the three possible values for x−1x-1 are:

x−1=−2(1)=−2x-1 = -2(1) = -2 x−1=−2ωx-1 = -2\omega x−1=−2ω2x-1 = -2\omega^2

Solving for xx in each case:

  1. x=1−2=−1x = 1 - 2 = -1
  2. x=1−2ωx = 1 - 2\omega
  3. x=1−2ω2x = 1 - 2\omega^2

Thus, the roots of the equation are −1,1−2ω, and 1−2ω2-1, 1 - 2\omega, \text{ and } 1 - 2\omega^2.

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