sin（π/4+α)=1/4,则sin2α=?_数学解答

sin（π/4+α)=1/4,则sin2α=?

人气：351 ℃　时间：2020-02-04 15:44:27

解答

sin2α
= -cos(2α+π/2)
= -cos2(π/4+α)
= -[ 1-2sin²（π/4+α)]
= -( 1-(1/4)² )
= -15/16