How to simplify this expression?


where $$\theta_i = \frac{2^{i-1}\pi}{2^n+1}$$

  • $\begingroup$ what ? how? could you please recheck your calculations? $\endgroup$ – maveric Feb 13 at 17:28
  • $\begingroup$ seriously, why is this question being downvoted? $\endgroup$ – maveric Feb 13 at 17:33
  • $\begingroup$ Can you show some of your efforts? This will help us pick up where you left off :) $\endgroup$ – YiFan Feb 13 at 22:52
  • $\begingroup$ i tried with roots of unity. with n=3, formed an equation whose roots are square the given angles, but one angle tan 3pi/9 was also root. but its value was known so i could find. but then not able to generalize for n. $\endgroup$ – maveric Feb 14 at 3:46
  • $\begingroup$ Getting answer $3....$ $\endgroup$ – jacky Feb 14 at 11:26

Given $\displaystyle \theta_{i}=\frac{2^{i-1}}{2^n+1}$

Using the Identity $$\sec^2(\theta_{i})=4\csc^2(2\theta_{i})-\csc^2(\theta_{i})$$ and using $\displaystyle \theta_{i+1}=2\theta_{i}.$

and we have $$\csc^2(\theta_{n+1})=\csc^2(\theta_{1}).$$

$$\displaystyle \sum^{n}_{i=1}\sec^2(\theta_{i})=4\sum^{n}_{i=1}\csc^2(\theta_{i+1})-\sum^{n}_{i=1}$$



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