先由sin2x/cos^2x=8/3求出tanx,在根据二倍角公式求出tan2x
sin2x/cos^2x
=(2sinxcosx)/cos^2x
=2sinx/cosx
=2tanx=8/3
即tanx=4/3
所以tan2x=2tanx/[1-(tanx)^2]
=2*(4/3)/[1-(4/3)^2]=-24/7
先由sin2x/cos^2x=8/3求出tanx,在根据二倍角公式求出tan2x
sin2x/cos^2x
=(2sinxcosx)/cos^2x
=2sinx/cosx
=2tanx=8/3
即tanx=4/3
所以tan2x=2tanx/[1-(tanx)^2]
=2*(4/3)/[1-(4/3)^2]=-24/7