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Which of the following is equivalent to 
sec ((2pi)/(7)) ?

sec ((9pi)/(7))

sec ((19 pi)/(7))

sec ((12 pi)/(7))

sec ((5pi)/(7))

Which of the following is equivalent to sec2π7 \sec \frac{2 \pi}{7} ?\newlinesec9π7 \sec \frac{9 \pi}{7} \newlinesec19π7 \sec \frac{19 \pi}{7} \newlinesec12π7 \sec \frac{12 \pi}{7} \newlinesec5π7 \sec \frac{5 \pi}{7}

Full solution

Q. Which of the following is equivalent to sec2π7 \sec \frac{2 \pi}{7} ?\newlinesec9π7 \sec \frac{9 \pi}{7} \newlinesec19π7 \sec \frac{19 \pi}{7} \newlinesec12π7 \sec \frac{12 \pi}{7} \newlinesec5π7 \sec \frac{5 \pi}{7}
  1. Understand Secant Function Properties: Understand the properties of the secant function. The secant function, sec(θ)\sec(\theta), is periodic with a period of 2π2\pi. This means that sec(θ)=sec(θ+2πk)\sec(\theta) = \sec(\theta + 2\pi k) for any integer kk. We will use this property to find an equivalent expression for sec(2π7)\sec(\frac{2\pi}{7}).
  2. Compare with Options: Compare the given options with the original expression sec(2π7)\sec\left(\frac{2\pi}{7}\right) by adding multiples of 2π2\pi to the original angle and see which option matches. We will start with sec(9π7)\sec\left(\frac{9\pi}{7}\right) and check if it is equivalent to sec(2π7)\sec\left(\frac{2\pi}{7}\right).
  3. Check sec(9π7)\sec\left(\frac{9\pi}{7}\right): Add 2π2\pi to the original angle 2π7\frac{2\pi}{7} to see if it matches sec(9π7)\sec\left(\frac{9\pi}{7}\right). The calculation is 2π7+2π=2π+14π7=16π7\frac{2\pi}{7} + 2\pi = \frac{2\pi + 14\pi}{7} = \frac{16\pi}{7}. This does not match sec(9π7)\sec\left(\frac{9\pi}{7}\right), so sec(9π7)\sec\left(\frac{9\pi}{7}\right) is not equivalent to sec(2π7)\sec\left(\frac{2\pi}{7}\right).
  4. Check sec(19π7)\sec\left(\frac{19\pi}{7}\right): Check sec(19π7)\sec\left(\frac{19\pi}{7}\right) by adding 2π2\pi to the angle 2π7\frac{2\pi}{7} twice. The calculation is 2π7+2×2π=2π7+28π7=30π7\frac{2\pi}{7} + 2\times2\pi = \frac{2\pi}{7} + \frac{28\pi}{7} = \frac{30\pi}{7}. This simplifies to 2×14π+2π7=28π+2π7=30π7\frac{2\times14\pi + 2\pi}{7} = \frac{28\pi + 2\pi}{7} = \frac{30\pi}{7}. This does not match sec(19π7)\sec\left(\frac{19\pi}{7}\right), so sec(19π7)\sec\left(\frac{19\pi}{7}\right) is not equivalent to sec(2π7)\sec\left(\frac{2\pi}{7}\right).
  5. Check sec(12π7)\sec\left(\frac{12\pi}{7}\right): Check sec(12π7)\sec\left(\frac{12\pi}{7}\right) by subtracting 2π2\pi from the angle 2π7\frac{2\pi}{7}. The calculation is 2π72π=2π14π7=12π7\frac{2\pi}{7} - 2\pi = \frac{2\pi - 14\pi}{7} = \frac{-12\pi}{7}. This does not match sec(12π7)\sec\left(\frac{12\pi}{7}\right), so sec(12π7)\sec\left(\frac{12\pi}{7}\right) is not equivalent to sec(2π7)\sec\left(\frac{2\pi}{7}\right).
  6. Check sec(5π7)\sec\left(\frac{5\pi}{7}\right): Check sec(5π7)\sec\left(\frac{5\pi}{7}\right) by adding 2π2\pi to the angle 2π7\frac{2\pi}{7} three times. The calculation is 2π7+3×2π=2π7+42π7=44π7\frac{2\pi}{7} + 3\times2\pi = \frac{2\pi}{7} + \frac{42\pi}{7} = \frac{44\pi}{7}. This simplifies to 6×7π+2π7=42π+2π7=44π7\frac{6\times7\pi + 2\pi}{7} = \frac{42\pi + 2\pi}{7} = \frac{44\pi}{7}. This does not match sec(5π7)\sec\left(\frac{5\pi}{7}\right), so sec(5π7)\sec\left(\frac{5\pi}{7}\right) is not equivalent to sec(2π7)\sec\left(\frac{2\pi}{7}\right).
  7. Correct Approach for Finding kk: Realize that there was a mistake in the previous steps. We need to find a kk such that 2π7+2πk=\frac{2\pi}{7} + 2\pi k = one of the given options. We should have been looking for a kk that makes the expression 2π7+2πk7=\frac{2\pi}{7} + \frac{2\pi k}{7} = one of the given options. We will re-evaluate the options with this corrected approach.

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