四.添加辅助线O4, O4:y=0,x从0→2, x+y=2x aP ay =e cos y, A(2,0 00 =e coste a 原式 L+0404 x' dxdy- e sin ydx +(e cos y+ a)dy D 0A 3 2o2 cos 6 ·rur K心四. x y O A(2,0) x y 2x 2 2 + = 添加辅助线OA, OA: y = 0, x从0 → 2, e cos y, y P x =   cos , 2 e y x x Q x = +   =  −  L+OA OA 原式=  −  + + O A x x D dy x x dxdy e ydx e y ) 3 sin ( cos 2 2   =      2cos 0 2 2 2 0 d r cos rdr