(2000²-2000+1)/(2000的平方-2000*1999+1999的平方)
=[(2000x(2000-1)+1]/[(2000x(2000-1999)+1999的平方]
=[2000x1999+1]/[(2000+1999的平方]
=[2000x1999+1]/[(1999+1999的平方+1]
=[2000x1999+1]/[(1+1999)x1999+1]
=[2000x1999+1]/[2000x1999+1]
=1