若sin(a-π/6)=1/3,则cos(2a+π/3)的值为( )A.√2/2 B.1 C.√2 D.√3

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若sin(a-π/6)=1/3,则cos(2a+π/3)的值为( )A.√2/2 B.1 C.√2 D.√3
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若sin(a-π/6)=1/3,则cos(2a+π/3)的值为( )A.√2/2 B.1 C.√2 D.√3
若sin(a-π/6)=1/3,则cos(2a+π/3)的值为( )
A.√2/2 B.1 C.√2 D.√3

若sin(a-π/6)=1/3,则cos(2a+π/3)的值为( )A.√2/2 B.1 C.√2 D.√3
cos(2a+π/3)=cos[(a-π/6)+(a+π/2)]
cos(a-π/6)=开根号1-sin(a-π/6)*sin(a-π/6)
sin(a-π/6)展开求解

此题错误,若按此题,结果是 -0.9332,无此选项;若改成求cos(2a-3π),则结果为7/9,也无此选项。检查一下,是题目抄错,还是原题错误。