xcosy = sin(x+y)cosy+x(-siny)y' = cos(x+y)(1+y')cosy-xsiny y'=cos(x+y)+cos(x+y)y'y' = (cosy-cos(x+y))/判蔽(xsiny+cos(x+y))第掘尺州二个看不清求什困芹么