sinx+cosx=√2(√2/2*sinx+√2/2cosx)
=√2(sinxcosπ/4+cosxsinπ/4)
=√2sin(x+π/4)不懂第二步sinxcosπ/4+cosxsinπ/4怎么来的就是√2/2=sinπ/4=cosπ/4对哦。。。那sinx*cosπ/4+cosx*sinπ/4又变成sin(x+π/4)sin(a+b)=? 学过吗好像没有=sinacosb+cosasinb 别追问了