例21(1)设=l,u=ex,v=sinx,求 dz dz (2)设=f(x,e),求 L 解2=02.a+0. dx au dx ay dx v·e+ll·coSx e(sin x+cos x) ,→x (2)令y=e,则=f(x,y) J dz af, af dy9 21 (1) , , sin , ; (2) ( , ), . x x dz z uv u e v x dx dz z f x e dx − = = = = 例 设 求 设 求 z u v x dz z du z dv dx u dx v dx   =  +    解 cos x =  +  v e u x (sin cos ). x = + e x x (2) , ( , ) x y e z f x y − 令 则 = = z x y x dz f f dy dx x y dx    = +    . x x y f e f − = −  