方法一：sin(x+π/4)=sinxcosπ/4+cosxsinπ/4=(√2/2)sinx+(√2/2)cosx=cosxcosπ/4+sinxsinπ/4=cos(π/4-x)方法二：因为(x+π/4)+(π/4-x)=π/2、即(x+π/4)=π/2-(π/4-x)所以sin(x+π/4)=sin[π/2-(π/4-x)]=co...