已知sinα=23,则cos(3π−2α)等于(  ) A.−53 B.19 C.-19 D.53

问题描述:

已知sinα=

2
3
,则cos(3π−2α)等于(  )
A.
5
3

B.
1
9

C. -
1
9

D.
5
3

∵sinα=

2
3

∴cos(3π-2α)=cos[2π+(π-2α)]
=cos(π-2α)=-cos2α=-(1-2sin2α)
=-1+2×
4
9
=-
1
9

故选C