1/2a-[2a-(2/3)a^2]-[-(3/2)a+(1/3)a^2]
=1/2a-2a+2/3a²+3/2a-1/3a²
=(1/2-2+3/2)a+(2/3-1/3)a²
=(1/3)a²
=1/3×(-1/4)²
=1/3×1/16
=1/48
1/2a-[2a-(2/3)a^2]-[-(3/2)a+(1/3)a^2]
=1/2a-2a+2/3a²+3/2a-1/3a²
=(1/2-2+3/2)a+(2/3-1/3)a²
=(1/3)a²
=1/3×(-1/4)²
=1/3×1/16
=1/48