因为a^2-2006a+1=0 所以a^2+1=2006a a^2-2005a+2006/(a^2+1) =a^2-2005a+2006/2006a =a^2-2005a+1/a =a-1+1/a =(a^2-a+1)/a =2005a/a =2005
+z？
