2(3a平方b-ab平方)-4a平方b+5-3(2/3a平方b-ab2次方+4)
=6a^2b-2ab^2-4a^2b+5-2a^2b+3ab^2-12
=ab^2-7
=2*(-1/2)^2-7
=1/2-7
=-13/2