已知x∈(-π2,0),cosx=45,則tan2x等于( ?。?A.724 B.-724 C.247 D.-247
已知x∈(-
,0),cosx=
,則tan2x等于( ?。?br/>A.
B. -
C.
D. -
數(shù)學人氣:586 ℃時間:2020-05-19 09:47:18
優(yōu)質(zhì)解答
∵cosx=
,x∈(-
,0),
∴sinx=-
.∴tanx=-
.
∴tan2x=
=
=-
×
=-
.
故選D.
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