Agustín Valverde Ramos edited Soluci_n_begin_aligned_cos__.tex  over 8 years ago

Commit id: 48327d716bbca91b9a6fbc14dd0ed6b27f0a9609

deletions | additions      

       

Solución:  \[  \begin{aligned}  \cos(5\theta) & = \mathrm{Re}((\cos \theta+\mathrm{i}\sin\theta)^5) = \\  & = \mathrm{Re}(\cos^5 \theta+5\mathrm{i}\cos^4\theta\sin\theta  −10\cos^3 \theta\sin^2 \theta  −10\mathrm{i}\cos^2\theta\sin^3\theta  +5\cos \theta\sin^4 \theta  +\mathrm{i}\sin^5\theta) = \\  & = \cos^5 \theta−10\cos^3 \theta\sin^2 \theta+5\cos \theta\sin^4 \theta = \\  & = \cos^5 \theta−10\cos^3 \theta(1-\cos^2\theta)+5\cos \theta(1-\cos^2\theta)^2 = \\  & = \cos^5 \theta−10\cos^3 \theta+10\cos^5\theta+5\cos \theta(1-2\cos^2\theta+\cos^4\theta) = \\  & = \cos^5 \theta−10\cos^3 \theta+10\cos^5\theta+5\cos \theta-10\cos^3\theta+5\cos^5\theta = \\  & = 16\cos^5 \theta−20\cos^3 \theta+5\cos \theta  \end{aligned}  \]