又证明（3) A(v) =yx+1乙x+1-yx·Zx =yx+1x+1yx+x+y+x-yxx =ysHxm-zx)+s-ys)is yxtAZx +ZAyx 经济数学 微积分 ( ) x x x x x x y z y z y z =  −    +1 +1 x x x x x x x x = y z − y z + y z − y z +1 +1 +1 +1 又证明（3） ( ) ( ) x x x x x x = y z − z + y − y z +1 +1 +1 x x x x y Δz z Δy = +1 +