sin(2x-派/2)= sin(2x-派/2)=

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sin(2x-派/2)=sin(2x-派/2)=sin(2x-派/2)=sin(2x-派/2)=sin(2x-派/2)=sin(2x-派/2)=方法一:sin(2x-π/2)=sin2x*cosπ/2

sin(2x-派/2)= sin(2x-派/2)=
sin(2x-派/2)=
sin(2x-派/2)=

sin(2x-派/2)= sin(2x-派/2)=
方法一:sin(2x-π/2)=sin2x*cosπ/2-cos2x*sinπ/2=-cos2x;(运用公式)
方法二:sin(2x-π/2)=-cos2x;(运用口诀:横不变,纵变;符号看象限)

sin(2x-π/2)=sin2x*cosπ/2-cos2x*sinπ/2=-cos2x

原式=cos2x=1-2(cosx)^2