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

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

人气：272 ℃　时间：2019-09-27 05:45:55

解答

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