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Which of the following is equivalent to 
sin ((pi)/(7)) ?

sin ((13 pi)/(7))

sin ((8pi)/(7))

sin(-(pi)/(7))

sin ((15 pi)/(7))

Which of the following is equivalent to sinπ7 \sin \frac{\pi}{7} ?\newlinesin13π7 \sin \frac{13 \pi}{7} \newlinesin8π7 \sin \frac{8 \pi}{7} \newlinesin(π7) \sin \left(-\frac{\pi}{7}\right) \newlinesin15π7 \sin \frac{15 \pi}{7}

Full solution

Q. Which of the following is equivalent to sinπ7 \sin \frac{\pi}{7} ?\newlinesin13π7 \sin \frac{13 \pi}{7} \newlinesin8π7 \sin \frac{8 \pi}{7} \newlinesin(π7) \sin \left(-\frac{\pi}{7}\right) \newlinesin15π7 \sin \frac{15 \pi}{7}
  1. Properties of Sine Function: Understand the properties of the sine function. The sine function has a period of 2π2\pi, which means sin(θ)=sin(θ+2πk)\sin(\theta) = \sin(\theta + 2\pi k) for any integer kk. Also, sin(θ)=sin(πθ)\sin(\theta) = \sin(\pi - \theta) for any angle θ\theta.
  2. Evaluate sin(13π7)\sin\left(\frac{13\pi}{7}\right): Evaluate sin(13π7)\sin\left(\frac{13\pi}{7}\right).\newlineSince 13π7=π+6π7\frac{13\pi}{7} = \pi + \frac{6\pi}{7}, we can use the property sin(θ)=sin(θ+2πk)\sin(\theta) = \sin(\theta + 2\pi k) with k=1k = -1 to find an equivalent expression.\newlinesin(13π7)=sin(13π72π)=sin(13π714π7)=sin(π7)\sin\left(\frac{13\pi}{7}\right) = \sin\left(\frac{13\pi}{7} - 2\pi\right) = \sin\left(\frac{13\pi}{7} - \frac{14\pi}{7}\right) = \sin\left(-\frac{\pi}{7}\right).\newlineThis is not equivalent to sin(π7)\sin\left(\frac{\pi}{7}\right) because sin(θ)\sin(\theta) is not generally equal to sin(θ)\sin(-\theta).
  3. Evaluate sin(8π7)\sin\left(\frac{8\pi}{7}\right): Evaluate sin(8π7)\sin\left(\frac{8\pi}{7}\right).\newlineSince 8π7=π+π7\frac{8\pi}{7} = \pi + \frac{\pi}{7}, we can use the property sin(θ)=sin(πθ)\sin(\theta) = \sin(\pi - \theta).\newlinesin(8π7)=sin(ππ7)=sin(6π7)\sin\left(\frac{8\pi}{7}\right) = \sin\left(\pi - \frac{\pi}{7}\right) = \sin\left(\frac{6\pi}{7}\right).\newlineThis is not equivalent to sin(π7)\sin\left(\frac{\pi}{7}\right) because 6π7\frac{6\pi}{7} is not the same angle as π7\frac{\pi}{7}.
  4. Evaluate sin(π7)\sin\left(-\frac{\pi}{7}\right): Evaluate sin(π7)\sin\left(-\frac{\pi}{7}\right). Using the odd function property of sine, which is sin(θ)=sin(θ)\sin(-\theta) = -\sin(\theta), we get: sin(π7)=sin(π7)\sin\left(-\frac{\pi}{7}\right) = -\sin\left(\frac{\pi}{7}\right). This is not equivalent to sin(π7)\sin\left(\frac{\pi}{7}\right) because of the negative sign.
  5. Evaluate sin(15π7)\sin\left(\frac{15\pi}{7}\right): Evaluate sin(15π7)\sin\left(\frac{15\pi}{7}\right).\newlineSince 15π7=2π+π7\frac{15\pi}{7} = 2\pi + \frac{\pi}{7}, we can use the property sin(θ)=sin(θ+2πk)\sin(\theta) = \sin(\theta + 2\pi k) with k=1k = -1 to find an equivalent expression.\newlinesin(15π7)=sin(15π72π)=sin(15π714π7)=sin(π7)\sin\left(\frac{15\pi}{7}\right) = \sin\left(\frac{15\pi}{7} - 2\pi\right) = \sin\left(\frac{15\pi}{7} - \frac{14\pi}{7}\right) = \sin\left(\frac{\pi}{7}\right).\newlineThis is equivalent to sin(π7)\sin\left(\frac{\pi}{7}\right) because we have subtracted a full period of the sine function.

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