化简:①7m-3(m-2n)= ②-(x^2-y^2)-4(二分之一x^2-y^2)=

问题描述:

化简:①7m-3(m-2n)= ②-(x^2-y^2)-4(二分之一x^2-y^2)=

①7m-3(m-2n)==7m-3m+6n=4m+6n
②-(x^2-y^2)-4(二分之一x^2-y^2)=-x^2+y^2-2x^2+4y^2=-3x^2+5y^2
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