sinx/cosx=tanx=4/3
sinx=4/3*cosx
sin²x+cos²x=1
所以cos²x=9/25
sin2x
=2sinxcosx
=2(4/3*cosx)cosx
=8/3cos²x
=24/25
cos2x=2cos²x-1=-7/25
tan2x=2tanx/(1-tan²x)=-24/7