(1)1/2n+3/5n^2-0.4n^2
(2)3x-4x^2+7-3x^2+2x-1
(3)2x^2y+5xy^2-3X^2y^2-4xy2
(4)4ab-3a^2-ab+b^2+a^2-3ab-2b+2a^2
(1)1/2n+3/5n^2-0.4n^2
(2)3x-4x^2+7-3x^2+2x-1
(3)2x^2y+5xy^2-3X^2y^2-4xy2
(4)4ab-3a^2-ab+b^2+a^2-3ab-2b+2a^2
(1)原式= 1/2n+(3/5-0.4)n^2 =1/2n+1/5n^2
(2)原式= (-4-3)x^2+(3+2)x+(7-1) = -7x^2+5x+6
(3)原式= -3x^2y^2+2x^2y+(5-4)xy^2 = -3x^2y^2+2x^2y+xy^2
(4)原式= (-3+1+2)a^2+(4-1-3)ab+b^2+2b = b^2+2b