=7ab-(3a^2b^2+7-2(8ab^2+3a^2b^2-3/2-7/2ab)
=7ab-(3a^2b^2+7-16ab^2-6a^2b^2+3+7ab)
=7ab-3a^2b^2-10+16ab^2+6a^2b^2-7ab
=3a^2b^2+16ab^2-10若a=1/2，b=4，这个代数式的值为？若a=1/2，b=4，此代数式的值为？