(1999+2000*1998)/(1999*2000-1)
= [1999+(1999+1)*(1999-1)] / (1999*2000-1)
= (1999+1999*1999-1) / (1999*2000-1)
= [1999*(1+1999)-1] / (1999*2000-1)
= (1999*2000-1) / (1999*2000-1)
= 1
(1999+2000*1998)/(1999*2000-1)
= [1999+(1999+1)*(1999-1)] / (1999*2000-1)
= (1999+1999*1999-1) / (1999*2000-1)
= [1999*(1+1999)-1] / (1999*2000-1)
= (1999*2000-1) / (1999*2000-1)
= 1