Practicing Success
Solve cos36° . cos72° . cos108° . cos144° |
\(\frac{1}{16}\) -\(\frac{1}{16}\) \(\frac{1}{32}\) \(\frac{1}{8}\) |
\(\frac{1}{16}\) |
cos36° cos72° cos108° cos144° = cos36° .cos72°. (- cos72°). (- cos36°) = (cos36° cos72°)2 = (cos \(\frac{π}{5}\) cos \(\frac{2π}{5}\))2 If θ = \(\frac{π}{2^4 + 1}\) = \(\frac{1}{2^4}\) So, (Cos \(\frac{π}{5}\) cos2\(\frac{π}{5}\))2 ⇒ (\(\frac{1}{(2)^2}\))2 = \(\frac{1}{16}\) |