Найдите \(tg2x,\) если \(cosx=\frac{5}{8},\) \(\frac{3\pi}{4}\lt x\lt 2\pi.\)

• \(-\frac{5\sqrt{39}}{7}\)
• \(\frac{5\sqrt{39}}{7}\)
• \(-\frac{5\sqrt{11}}{7}\)
• \(\frac{5\sqrt{11}}{7}\)