2a的平方b(a+2b-1) =2a^3b+4a^2b^2-2a^2b
(-1/3一xy)(12xy^2-6x^2y)=-4xy^2+2x^2y-12x^2y^3+6x^3y
-2x的三次方(3x的平方-5x-6)=-6x^5+10x^4+12x^3
2a的平方b(a+2b-1) =2a^3b+4a^2b^2-2a^2b
(-1/3一xy)(12xy^2-6x^2y)=-4xy^2+2x^2y-12x^2y^3+6x^3y
-2x的三次方(3x的平方-5x-6)=-6x^5+10x^4+12x^3