yyyy 2-1 (6)z=(1+xyy: 解会0*y=少0*y 等-8司 =0+y0+ (7)u=x: 解 (8)u=arctan(x-y): 解：0x- x1+(x-y)2 0-2-y)- y1+(K-y)1 ou (x-y)In(x-y) 1+(-y)2