设-π/2设-π/2
设-π/2由题意:cosxcosy-sinxsiny+cosxcosy+sinxsiny=2cos²x+½即:cosxcosy-cos²x=¼∴cosy=1/4cosx +cosx≧1∴cosy=1,得:y=0代入y解得:x=±π/3