⑩天掌 Teaching Plan on Advanced Mathematics 1.5 +1 D2 33 x≤z ≤y≤1 原式=hdtn/(x,y,+ n'dxr-at dzl-wxf(x,],z)dy tianjin Polytechnic univerityTianjin Polytechnic University Teaching Plan on Advanced Mathematics    − 1 + 1 0 1 2 2 2 ( , , ) z x x x dx dz f x y z dy. D2：    −     + 1 1 2 2 2 z x y x z x D2 =    + 1 0 1 0 0 ( , , ) 2 dx dz f x y z dy x 原式