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Given the equation 2 3theta − 1 = 0.

Mathematics

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Step-by-step solution

4 steps
  1. Isolate cos⁡3θ\cos 3\theta.

    Given the equation 2cos⁡3θ−1=02 \cos 3\theta - 1 = 0.
    Add 1 to both sides:

    2cos⁡3θ=12 \cos 3\theta = 1

    Divide by 2:

    cos⁡3θ=12\cos 3\theta = \frac{1}{2}
  2. Find the principal value for 3θ3\theta.

    Let α\alpha be the principal value such that cos⁡α=12\cos \alpha = \frac{1}{2}.

    α=arccos⁡(12)\alpha = \arccos\left(\frac{1}{2}\right) α=60∘\alpha = 60^\circ
  3. Find all possible values for 3θ3\theta within the given range.

    The range for θ\theta is 0∘≤θ≤360∘0^\circ \le \theta \le 360^\circ.
    Therefore, the range for 3θ3\theta is 3×0∘≤3θ≤3×360∘3 \times 0^\circ \le 3\theta \le 3 \times 360^\circ, which is 0∘≤3θ≤1080∘0^\circ \le 3\theta \le 1080^\circ.

    Since cos⁡3θ\cos 3\theta is positive, 3θ3\theta lies in the first and fourth quadrants.
    The general solutions for cos⁡x=cos⁡α\cos x = \cos \alpha are x=2nπ±αx = 2n\pi \pm \alpha (in radians) or x=n⋅360∘±αx = n \cdot 360^\circ \pm \alpha (in degrees), where nn is an integer.

    For n=0n=0:
    3θ=60∘3\theta = 60^\circ
    3θ=360∘−60∘=300∘3\theta = 360^\circ - 60^\circ = 300^\circ

    For n=1n=1:
    3θ=360∘+60∘=420∘3\theta = 360^\circ + 60^\circ = 420^\circ
    3θ=360∘+(360∘−60∘)=360∘+300∘=660∘3\theta = 360^\circ + (360^\circ - 60^\circ) = 360^\circ + 300^\circ = 660^\circ

    For n=2n=2:
    3θ=2⋅360∘+60∘=720∘+60∘=780∘3\theta = 2 \cdot 360^\circ + 60^\circ = 720^\circ + 60^\circ = 780^\circ
    3θ=2⋅360∘+(360∘−60∘)=720∘+300∘=1020∘3\theta = 2 \cdot 360^\circ + (360^\circ - 60^\circ) = 720^\circ + 300^\circ = 1020^\circ

    All these values are within the range 0∘≤3θ≤1080∘0^\circ \le 3\theta \le 1080^\circ.

  4. Divide each value of 3θ3\theta by 3 to find θ\theta.

    θ1=60∘3=20∘\theta_1 = \frac{60^\circ}{3} = 20^\circ θ2=300∘3=100∘\theta_2 = \frac{300^\circ}{3} = 100^\circ θ3=420∘3=140∘\theta_3 = \frac{420^\circ}{3} = 140^\circ θ4=660∘3=220∘\theta_4 = \frac{660^\circ}{3} = 220^\circ θ5=780∘3=260∘\theta_5 = \frac{780^\circ}{3} = 260^\circ θ6=1020∘3=340∘\theta_6 = \frac{1020^\circ}{3} = 340^\circ

    The values of θ\theta are 20∘,100∘,140∘,220∘,260∘,340∘\boxed{20^\circ, 100^\circ, 140^\circ, 220^\circ, 260^\circ, 340^\circ}.

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