sinx+siny=1/3∴sinx=1/3-sinysinx-(cosy)^2=sinx-[1-(siny)^2]=sinx+(siny)^2=(siny)^2-siny+1=(siny-1/2)^2+3/4 ≥ 3/4,即最小值3/4； -1≤ siny ≤1当siny=-1时,最大值：(-1-1/2)^2+3/4=(3/2)^2+3/4=3...