1/2(a-a^2+1-4a^3)-3/2(-a+7a^2-2a^3)
=1/2a-1/2a^2+1/2-2a^3+3/2a-21/2a^2+3a^3
=1/2+(1/2a+3/2a)-(1/2+21/2a^2)a^2+(3a^3-2a^3)
=1/2+2a-11a^2+a^3