计算：5（3a^2b-ab^2)-4(-ab^2+3a^2b)其中a=-2b=3
问题描述：
计算：5（3a^2b-ab^2)-4(-ab^2+3a^2b)其中a=-2b=3
答
5(3a^2b-ab^2)-4(-ab^2+3a^2b)
=15a^2b-5ab^2+4ab^2-12a^2b
=15a^2b-12a^2b-5ab^2+4ab^2
=3a^2b-ab^2
=ab(3a-b)
=-2*3*[3*(-2)-3]
=-6*(-9)
=54那么3x^2-[x^2-2(3x-x^2)]其中x=-73x^2-[x^2-2(3x-x^2)]=3x^2-[x^2-6x+2x^2]=3x^2-[3x^2-6x]=3x^2-3x^2+6x=6x=6*(-7)=-42计算:-（2x^2+xy+3y^2)-3(x^2-xy)-（2x^2+xy+3y^2)-3(x^2-xy)=-2x^2-xy-3y^2-3x^2+3xy=-2x^2-3x^2-xy+3xy-3y^2=-5x^2+2xy-3y^2