⑩天掌 Teaching Plan on Advanced Mathematics 4.性质 (1).If(x,y)±g(x,y)d=,f(x,y)d±,(x,y)d (2J6(,y)=kf(x,)(为常数 (3), /(x, y)ds=L f(x,y)ds+l,f(,y)ds (L=L1+L2) tianjin Polytechnic univerityTianjin Polytechnic University Teaching Plan on Advanced Mathematics 4.性质 (1) [ ( , ) ( , )] ( , ) ( , ) .     =  L L L f x y g x y ds f x y ds g x y ds (2) kf (x, y)ds k f (x, y)ds (k为常数). L L = (3) ( , ) ( , ) ( , ) . 1 2    = + L L L f x y ds f x y ds f x y ds ( ). L = L1 + L2