cos80=-cos100=-k
cos100<0则k<源扮0
sin²80+cos²80=1
且sin80>0
所以sin80=√(1-k²)
所以tan(-80)
=-tan80
=-sin80/冲裂cos80
=√(1-k²雹判灶)/k
cos100°=k
cos(180-100)=-k
cos(-80)=-k
tan(-80°)=(跟绝肢桐下1-k^2)/并坦饥敬-k
解 :
cos(-80)= cos80=-cos100=-k
sin(-80)=-sin80=-√扮禅斗袭败(1-k²)
tan(-80)=sin(-80)/cos(-80)=√(1-k²厅磨)/k