Thursday, November 8, 2018

sequences and series - trigonometric summation with arithmetic progression of angles and coefficients

How can we sum up sin and cos series when the angles and also coefficients are in arithmetic progression?
Such as cos(x)+2cos(2x)+3cos(3x)+.......+ncos(nx)

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analysis - Injection, making bijection

I have injection $f \colon A \rightarrow B$ and I want to get bijection. Can I just resting codomain to $f(A)$? I know that every function i...