三角abc表示3abc,方框xwyz表示-4x^yw^z,求mn2乘nm25

a^3+b^3+c^3=3abc a^3+b^3+c^3-3abc=0 (a+b)^3+c^3-3a^2b-3ab^2-3abc=0 (a+b+c)[(a+b)^2-(a+b)c+c^2]-3ab(a+b+c)=0 (a+b+c)[(a+b)^2-(a+b)c+c^2-3ab]=0 (a+b+c)[a^2+b^2-ac-bc+c^2-ab]=0 (1/2)(a+b+c)[(a-b)^2+(b-c)...