格式难懂!
1.
1/5 (x=7)
2.
a²/(a-1)-a-1
=[a²-(a-1)(a+1)]/(a-1)
=1/(a-1)
3.
(x+2)/(x²-2x)-(x-1)/(x²-4x+4)
=(x+2)(x-2)/[x*(x-2)(x-2)]-x*(x-1)/[x*(x-2)(x-2)]
=[(x²-4)-(x²-x)]/[x*(x-2)(x-2)]
=(x-4)/(x³-4x²+4x)
4.
(a-2)/(a²+2a)+(a+1)/(a²+4a+4)
=(a-2)(a+2)/[a*(a+2)(a+2)]+a*(a+1)/[a*(a+2)(a+2)]
=[(a²-4)+(a²+a)]/[a*(a+2)(a+2)]
=(2a²+a-4)/(a³+4a²+4a)
5.
m/(m-n)-n/(m+n)+2mn/(m²-n²)
=m(m+n)/(m+n)(m-n)-n(m-n)/(m+n)(m-n)+2mn/(m+n)(m-n)
=[(m²+mn)-(mn-n²)+2mn]/(m+n)(m-n)
=(m+n)/(m-n)
6.
5m/(2m-n)-(m-n)/(n-2m)-6n/(2m-n)
=[5m+(m-n)-6n]/(2m-n)
=(6m-7n)/(2m-n)
7.
[(3x-6)/(x²-4)]/[(x+2)/(x²+4x+4)]-2
=[3/(x+2)]/[1/(x+2)]-2
=3-2
=1
8.
①
甲：1000(m+n)/(1000*2)=(m+n)/2
乙：1000*2/(1000/m+1000/n)=2mn/(m+n)
②
(m+n)/2-2mn/(m+n)
=[(m+n)(m+n)-4mn]/[2(m+n)]
=(m-n)²/[2(m+n)]
>0
乙的方式更合算!