题目

化简 sin{[(4n+1)π/4]+α}+cos{[(4n-1)π/4]-α},（n∈Z）

提问时间：2020-10-11

答案

sin{[(4n+1)π/4]+α}+cos{[(4n-1)π/4]-α}
=sin{nπ+[(π/4)+α]}+cos{nπ-[(π/4)+α]}
=sin(nπ)cos(π/4+α)+cos(nπ)sin(π/4+α)+cos(nπ)cos(π/4+α)+sin(nπ)sin(π/4+α)]
=cos(nπ)sin(π/4+α)+cos(nπ)cos(π/4+α) //sin(nπ)=0
=cos(nπ)[sin(π/4+α)+cos(π/4+α)]
=±[sin(π/4)cosα+cos(π/4)sinα+cos(π/4)cosα-sin(π/4)sinα] //cos(nπ)=±1
=±(√2)cosα //cos(π/4)=sin(π/4)=(√2)/2