①(2*2002²)/(2000²+2003²-5)
先计算分母(2000²+2003²-5)
2000²+2003²-5
=(2002-2)²+(2002+1)²-5
=2002²-2*2*2002+2²+2002²+2*1*2002+1²-5
=2002²-8008+4+2002²+4004+1-5
=2*2002²-4004
=2*2002*2002-2*2002
=2*2002*(2002-1)
=2*2002*2001
∴(2*2002²)/(2000²+2003²-5)
=(2*2002*2002)/(2*2002*2001)
=2002/2001
②99……9*99……9+99……9+10^n
=99……9*(99……9+1)+10^n
=99……9*10^n+10^n
=10^n*(99……9+1)
=10^n*10^n
=10^(2n)