问题描述：
(1) (a+2b/a-b)+(b/b-a)-(2a/a-b); (2) (y/x-y+z)+(2x+z/y-x-z)-(y-z/y-x-z); (3) （2/2a+3)+(3/3-2a)+(2a+15/4a^2-9); (4) (1/1-x)-(1/1+x)-（2x/1+x^2）+(-4x^3/1+x^4)
问题解答：
我来补答
(1) (a+2b/a-b)+(b/b-a)-(2a/a-b);
=(a+2b)/(a-b)-b/(a-b)-2a/(a-b)
=(a+2b-b-2a)/(a-b)
=(-a+b)/(a-b)
=-1
(2) (y/x-y+z)+(2x+z/y-x-z)-(y-z/y-x-z);
=y/(x-y+z)-(2x+z)/(x-y+z)+(y-z)/x-y+z)
=(y-2x-z+y-z)/(x-y+z)
=(-2x+2y-2z)/(x-y+z)
=-2
(3) （2/2a+3)+(3/3-2a)+(2a+15/4a^2-9);
=2/(2a+3)-3/(2a-3)+(2a+15)/(2a+3)(2a-3)
=[2(2a-3)-3(2a+3)+(2a+15)]/(2a+3)(2a-3)
=(4a-6-6a-9+2a+15)/(2a+3)(2a-3)
=0/(2a+3)(2a-3)
=0
(4) (1/1-x)-(1/1+x)-（2x/1+x^2）+(-4x^2/1+x^4)
=(1+x-1+x)/(1-x²)-（2x/1+x^2）+(-4x^2/1+x^4)
=[2x(1+x²)-2x(1-x²)]/(1-x^4)-4x^2/(1+x^4)
=4x²/(1-x^4)-4x²/(1+x^4)
=(4x²+4x^6-4x²+4x^6)/(1-x^8)
=8x^6/(1-x^8)
