3cosx = 8sinx/cosx
3cos^2 - 8sinx = 0
3 (1-sin^2) - 8sin=0
3sin^2 + 8sin - 3 = 0
(3sin-1)(sin+3) = 0
sinx = 1/3
x = arcsin(1/3)
有两个（1,2象限）~19.5 和160.5