Найдите \(tg2x,\) если \(cosx=\frac{5}{8},\) \(\frac{3\pi}{4}<x<2\pi.\)
\(-\frac{5\sqrt{39}}{7}\)
\(\frac{5\sqrt{39}}{7}\)
\(-\frac{5\sqrt{11}}{7}\)
\(\frac{5\sqrt{11}}{7}\)