-1/2a-2(a-1/2b^2)-(3/2a-1/3b^2)
=-1/2a-2a+b²-3/2a+1/3b²
=-4a+4/3b²
=4x2+4/3x(2/3)²
=8+4/3x4/9
=8+16/27
=8又16/27