若cos(-100°)=k,则tan80°等于( ) A.1−k2k B.−1−k2k C.1+k2k D.−1+k2k
问题描述:
若cos(-100°)=k,则tan80°等于( )
A.
1−k2
k
B. −
1−k2
k
C.
1+k2
k
D.
−
1+k2
k
答
∵cos(-100°)=k,
∴cos80°=-k,sin80°=
=
1−cos280°
1−k2
则tan80°=
=sin80° cos80°
1−k2
−k
故选B