已知a=20002000/20012001,b=20012001/20022002 c=200220002/200320

已知x=1/2 y=1/3 z=1/4 则(xx+yy-zz+2xy)/(xx-yy+zz-2xz) 得多少?
(xx+yy-zz+2xy)/(xx-yy+zz-2xz)
=[(x+y)^2-z^2]/[(x-z)^2-y^2]
=(x+y+z)(x+y-z)/(x-z+y)(x-z-y)
=(x+y+z)/(x-z-y)
=(1/2+1/3+1/4)/(1/2-1/4-1/3)
=-13
还有这到题:已知a=20002000/20012001,b=20012001/20022002
c=200220002/20032003,比较a,b,c的大小.
a=2000/2001 分子和分母同时除以10001
b=2001/2002 分子和分母同时除以10001
c=2002/2003 分子和分母同时除以10001
a=1-1/2001
b=1-1/2002
c=1-1/2003
因为1/2001>1/2002>1/2003
所以a