化简(每题4分,共20分)(1) 3x2+2x-5x2+3x
(2) 4(m2+n)+2(n-2m2)
(3) -3(2x2-xy)-(x2+xy-6)
(4) -(6a3b+2b2)+(4a3b-8b2)
(5)先化简,再求值:3x2y-[2x2y-(2xy-3x2y)]+3xy2,其中x=3,y=-
化简(每题4分,共20分)(1) 3x2+2x-5x2+3x
(2) 4(m2+n)+2(n-2m2)
(3) -3(2x2-xy)-(x2+xy-6)
(4) -(6a3b+2b2)+(4a3b-8b2)
(5)先化简,再求值:3x2y-[2x2y-(2xy-3x2y)]+3xy2,其中x=3,y=-