1.sin(wt+π/2)=sin(π-(wt+π/2))=sin(π/2-wt)=coswt
或者你可以干脆点,直接展开:sin(wt+π/2)=sinwt*cosπ/2+coswt*sinπ/2=0+coswt=coswt
2.是2倍.
因为2sinwt*coswt=sin2wt
1.sin(wt+π/2)=sin(π-(wt+π/2))=sin(π/2-wt)=coswt
或者你可以干脆点,直接展开:sin(wt+π/2)=sinwt*cosπ/2+coswt*sinπ/2=0+coswt=coswt
2.是2倍.
因为2sinwt*coswt=sin2wt