问题描述：
1.m^2-nc+mn-mc=(m^2+mn)-( )=( )( )
2.m^2-nc+mn-mc=(m^2-mc)-( )=( )( )
3.9-x^2+2xy-y^2=9-( )=( )^2-( )^2=( )( )
4.m^2=3m+3n-n^2=( )-( )=( )( )
5.x^2y-x^2z+y^2z-y^3=( )-( )=( )( )=( )( )( )
6.3a^2*x^3*y+6a^2*x^2*y^2+3a^2*xyz^2=3a^2*xy()=3a^2*xy[()-()]=3a^2*xy()()
2.m^2-nc+mn-mc=(m^2-mc)-( )=( )( )
3.9-x^2+2xy-y^2=9-( )=( )^2-( )^2=( )( )
4.m^2=3m+3n-n^2=( )-( )=( )( )
5.x^2y-x^2z+y^2z-y^3=( )-( )=( )( )=( )( )( )
6.3a^2*x^3*y+6a^2*x^2*y^2+3a^2*xyz^2=3a^2*xy()=3a^2*xy[()-()]=3a^2*xy()()
问题解答：
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