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Question
Math
Posted 12 months ago
n=1sin(nx)n\sum_{n=1}^{\infty} \frac{\sin (n x)}{n}
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Answer from Sia
Posted 12 months ago
Solution by Steps
step 1
The sum of the series is given by the formula derived from the asksia-ll calculator: n=1sin(nx)n=12i(log(1eix)log(eix(1+eix)))\sum_{n=1}^{\infty} \frac{\sin(nx)}{n} = \frac{1}{2} i \left(\log(1 - e^{ix}) - \log(e^{-ix}(-1 + e^{ix}))\right) when x x is a real number
step 2
The formula can be simplified using properties of logarithms: 12i(log(1eix)log(eix)+log(1+eix))\frac{1}{2} i \left(\log(1 - e^{ix}) - \log(e^{-ix}) + \log(-1 + e^{ix})\right)
step 3
Recognize that the complex logarithm can have multiple values due to the periodicity of the exponential function, but the principal value is taken here
step 4
The approximation of the sum is given by substituting e2.71828 e \approx 2.71828 and i i as the imaginary unit: 12i(log(12.71828ix)log(2.71828ix(1+2.71828ix)))\approx \frac{1}{2} i \left(\log(1 - 2.71828^{ix}) - \log(2.71828^{-ix}(-1 + 2.71828^{ix}))\right) when x x is a real number
Answer
n=1sin(nx)n=12i(log(1eix)log(eix(1+eix)))\sum_{n=1}^{\infty} \frac{\sin(nx)}{n} = \frac{1}{2} i \left(\log(1 - e^{ix}) - \log(e^{-ix}(-1 + e^{ix}))\right)
Key Concept
Summation of a trigonometric series involving sine and natural numbers
Explanation
The series is a special case of the Fourier series and can be expressed in terms of complex logarithms. The asksia-ll calculator provides a formula for the sum of the series, which involves complex numbers and the natural logarithm.

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