韦达定理tana*1/tana=1=(3k²-13)/33k²=16k²=16/3a在第三象限所以tana>0tana+1/tana=3k/3>0k>0k=4/√3tana+1/tana=4/√3tana=√3,tana=1/√3所以a=10π/3,a=19π/6所以sina=-√3/2,cosa=-1/2或sina=-1...