已知tanx=-12,则sin2x+3sinxcosx-1的值为( ) A.-13 B.2 C.-2或2 D.-2
已知tanx=-
,则sin
2x+3sinxcosx-1的值为( )
A. -
B. 2
C. -2或2
D. -2
数学人气:106 ℃时间:2019-11-13 23:37:23
优质解答
tanx=-
,即
=
−,cosx=-2sinx.
由sin
2x+cos
2x=1,得5sin
2x=1,
sin
2x=
所以原式=sin
2x-6sin
2x-1
=5sin
2x-1
=-1-1
=-2
故选D
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