y=sinx+cosx
=√2(√2/2*sinx+√2/2cosx)
=√2(sinxcosπ/4+cosxsinπ/4)
=√2sin(x+π/4)
对称轴sinsin是最值
所以sin(x+π/4)=±1
x+π/4=kπ+π/2
x=kπ+π/4x+π/4=3π/2，3π/2怎么得的？k=1这两步怎么得的？=√2(√2/2*sinx+√2/2cosx)=√2(sinxcosπ/4+cosxsinπ/4)我讨厌追问采纳我，重新问