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(m(m-1)-(m^2-n)=6
m^2-m-m^2+n=6
n-m=6
则n^2+m^2-2mn=36
n^2+m^2=36+2mn

(n^2+m^2)/2-mn
=18+mn-mn
=18
2.
x^m=5
x^(2m)=5^2
x^n=3
x^(3n)=3^3
x^(2m-3n)=x^2m/x^3n=5^2/3^3=25/27

1.
m(m-1)-(m^2-n)=6，n-m=6

（m^2+n^2/2）-mn=(1/2)(m^2+n^2-2mn)=(1/2)(n-m)^2=18

2.
x^2m-3n=[(x)^m]^2/[(y)^n]^3=25/27

m(m-1)-(m^2-n)=6，
m^2-m-m^2+n=6
n-m=6
（m^2+n^2/2）-mn
=(n^2-2mn+m^2)/2
=(n-m)^2/2
=6^2/2
=18

x^2m-3n
=x^2m/x^3n
=(x^m)^2/(x^n)^3
=5^2/3^3
=25/27

1
m(m-1)-(m^2-n)=6
m^2-m-m^2+n=6
n-m=6

（m^2+n^2/2）-mn
=(m^2+n^2-2mn)/2
=(n-m)^2/2
=6^2/2
=18

2
x^(2m-3n)
=x^(2m)/x^(3n)
=(x^m)^2/(x^n)^3
=5^2/3^3
=25/27

第一题感觉有问题
x^2m-3n=(x^m)^2/(x^n)^3=25/27

m(m-1)-(m^2-n)=6，
m^2-m-m^2+n=6
n-m=6
（m^2+n^2/2）-mn
=(n^2-2mn+m^2)/2