tan(π+2a)=-4/3 ===> tan2a=-4/3
tan2a=2tana/(1-tan^2 a)=-4/3
===> -3tana=2-2tan^2 a
===> 2tan^2 a-3tana-2=0
===> (2tana+1)(tana-2)=0
===> tana=-1/2,或者tana=2
因为a是第二象限角,则tana<0
所以,tana=-1/2
tan(π+2a)=-4/3 ===> tan2a=-4/3
tan2a=2tana/(1-tan^2 a)=-4/3
===> -3tana=2-2tan^2 a
===> 2tan^2 a-3tana-2=0
===> (2tana+1)(tana-2)=0
===> tana=-1/2,或者tana=2
因为a是第二象限角,则tana<0
所以,tana=-1/2