y=√2sin(x+π/4),
令 x+π/4=0,得x=-π/4,选 C怎么变得方程？y=sinx+cosx=√2[(√2/2)sinx+(√2/2)cosx]=√2[sinxcos(π/4)+cosxsin(π/4)]=√2sin(x+π/4)令 y=0，得 sin(x+π/4)=0，所以 x+π/4=kπ，x=-π/4+kπ所有的对称点为(-π/4+kπ，0)其中一个为(-π/4，0)y=√2sin(x+π/4)这个是怎么得到的？y=sinx+cosx=√2[(√2/2)sinx+(√2/2)cosx]=√2[sinxcos(π/4)+cosxsin(π/4)]=√2sin(x+π/4)