初二的20PTS

1.given that m/n=5/ 3
m/(m+n)+m/(m－n)+n^2/(n^2－m^2)=?
Sol
m/n=5/ 3
m/5=n/3=p
m=5p，n=3pm/(m+n)+m/(m
n)+n^2/(n^2－m^2)
=5p/(8p)+5p/(－2p)+9p^2/(9p^2－25p^2)
=5/8－5/2－9/16
=-39/16

2.given that x+ 1/x=2，x^2+1/x^2=?
Sol
x+1/x=2
x^2+2+1/x^2=4
x^2+1/x^2=2

3.find A&B in
(3－4)/[(x－1)(x－2)]=A/(x－1)+B/(x－2)
Sol
(3－4)/[(x－1)(x－2)]
=[(x－2)－(x－1)]/[(x－1)(x－2)]
=(x－2)/[(x－1)(x－2)]－(x－1)/[(x－1)(x－2)]
=1/(x－1)－1/(x－2)
A=1，B=－1