由万能公式,
sin2x=（2tanx)/[1+(tanx)^2]
=2*2 / 12*2
=4/5
cos2x=[1-(tanx)^2]/[1+(tanx)^2]
=(1-2*2)/(1+2*2)
=-3/5
tan2x=（2tanx)/[1-(tanx)^2]
=(2*2)/(1-2*2)
=-3/4