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Category: Trigonometry

Question-197073

Question Number 197073 by Abdullahrussell last updated on 07/Sep/23 Answered by Frix last updated on 07/Sep/23 sinπ7sin2π7sin3π7=xUsetrigonometricformulastoget14(cos3π14+cosπ14sinπ7)=x(1)Nowcomesthetrick$$\left(\mathrm{cos}\:\frac{\mathrm{3}\pi}{\mathrm{14}}\:+\mathrm{cos}\:\frac{\pi}{\mathrm{14}}\:−\mathrm{sin}\:\frac{\pi}{\mathrm{7}}\right)^{\mathrm{3}}…

Question-196816

Question Number 196816 by ERLY last updated on 01/Sep/23 Answered by MM42 last updated on 01/Sep/23 a)S=12+cost+cos2t++cosnt2sint2S=sint2+sin3t2sint2+sin5t2sin3t2++sin2n+12tsin2n12tS=sin(2n+12)t2sint2b)S=sint+sin3t++sin(2n+1)t$$\mathrm{2}{sintS}=\mathrm{1}−{cos}\mathrm{2}{t}+{cos}\mathrm{2}{t}−{cos}\mathrm{4}{t}+{cos}\mathrm{4}{t}−{cos}\mathrm{6}{t}+…+{cos}\mathrm{2}\left({n}+\mathrm{1}\right){t}−{cos}\mathrm{2}{nt}…