1.5x(2x^2-3x+4)
=10x^3-15x²+20x
2.-6x(x-3y)
=-6x²+18xy
3.-2a^2(1/2ab+b)
=-a³b-2a²b
4.(2/3x^2y-6xy)*1/2xy^2
=1/3x³y³-3x²y³