函数y=(sinx+cos)^2+2cos^2=sinx２+2sinxcosx+cosx２+2cosx２＝sinx２+2sinxcosx＋3cosx =[1-cos2x]/2+sin2x+[cos2x+1]/2*3=co2x+sin2x+2=根号2cos[x-π/4]+2 数形结合得：π/2+2kπ=