:(-4a^3)^2 - (2a)^2 * (1/2 a)^4 + (-2a^2)^3
=(-4)^2 * a^(3*2) - 4a^2 *1/16 *a^4 + (-2)^3 * a^(2*3)
=16*a^6 - 1/4 * a^(2+4) -8a^6
=31/4 *a^6