3(xy^2-x^2y）-2（xy+xy^2）+3x^2y
=3xy^2-3x^2y-2xy-2xy^2+3x^2y
=xy^2-2xy
5a^2-[a^2+（5a^2-2a）-2(a^2-3a）]
=5a^2-(a^2+5a^2-2a-2a^2+6a)
=5a^2-(4a^2-4a)
=a^2-4a
5ab-2[3ab-(4ab²+1/2ab)]-ab²的值,其中a=1/2,b=2/35ab-2[3ab-(4ab²+1/2ab)]-ab²=5ab-5ab+8ab²-ab²=7ab²其中a=1/2,b=2/37ab²=7*1/2*(2/3)²=14/9