Question

计算：5（3a^2b-ab^2)-4(-ab^2+3a^2b)其中a=-2b=3

Answer 1

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

追问

那么3x^2-[x^2-2(3x-x^2)]其中x=-7

追答

3x^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

追问

计算:-（2x^2+xy+3y^2)-3(x^2-xy)

追答

-（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

Answer 2

5（3a^2b-ab^2)-4(-ab^2+3a^2b)其中a=-2b=3
=15a²b-5ab²+4ab²-12a²b
=3a²b-ab²
=3*(-2)²*3-(-2)*3²
=36+18
=54