合并同类项:
(1)$3a^{2}-2a+4a^{2}-7a$; (2)$xy+7xy-5xy$;
(3)$-5a-2b+7a+9b$; (4)$2x-7y-5x+11y-1$;
(5)$-3a+2ab-4ab+2a$; (6)$4a^{2}+3b^{2}+2ab-2a^{2}+4b^{2}-ab$;
(7)$\frac {1}{2}m^{2}-3mn^{2}+4n^{2}+\frac {1}{2}m^{2}+5mn^{2}-4n^{2}$; (8)$-5m^{2}n+4mn^{2}-2mn+6m^{2}n+3mn$;
(9)$7a^{2}-2ab+b^{2}-5a^{2}-b^{2}-2a^{2}-ab$;
(10)$7ab-3a^{2}b^{2}+7+8ab^{2}+3a^{2}b^{2}-3-7ab-5ab^{2}$.
(1)$3a^{2}-2a+4a^{2}-7a$; (2)$xy+7xy-5xy$;
(3)$-5a-2b+7a+9b$; (4)$2x-7y-5x+11y-1$;
(5)$-3a+2ab-4ab+2a$; (6)$4a^{2}+3b^{2}+2ab-2a^{2}+4b^{2}-ab$;
(7)$\frac {1}{2}m^{2}-3mn^{2}+4n^{2}+\frac {1}{2}m^{2}+5mn^{2}-4n^{2}$; (8)$-5m^{2}n+4mn^{2}-2mn+6m^{2}n+3mn$;
(9)$7a^{2}-2ab+b^{2}-5a^{2}-b^{2}-2a^{2}-ab$;
(10)$7ab-3a^{2}b^{2}+7+8ab^{2}+3a^{2}b^{2}-3-7ab-5ab^{2}$.
答案：(1)$7a^{2}-9a$ (2)$3xy$ (3)$2a+7b$ (4)$-3x+4y-1$ (5)$-a-2ab$ (6)$2a^{2}+7b^{2}+ab$ (7)$m^{2}+2mn^{2}$ (8)$m^{2}n+4mn^{2}+mn$ (9)$-3ab$ (10)$3ab^{2}+4$
解析：
(1)$3{a}^{2}+4{a}^{2}-2a-7a=7{a}^{2}-9a$
(2)$xy+7xy-5xy=3xy$
(3)$-5a+7a-2b+9b=2a+7b$
(4)$2x-5x-7y+11y-1=-3x+4y-1$
(5)$-3a+2a+2ab-4ab=-a-2ab$
(6)$4{a}^{2}-2{a}^{2}+3{b}^{2}+4{b}^{2}+2ab-ab=2{a}^{2}+7{b}^{2}+ab$
(7)$\frac{1}{2}{m}^{2}+\frac{1}{2}{m}^{2}-3m{n}^{2}+5m{n}^{2}+4{n}^{2}-4{n}^{2}={m}^{2}+2m{n}^{2}$
(8)$-5{m}^{2}n+6{m}^{2}n+4m{n}^{2}-2mn+3mn={m}^{2}n+4m{n}^{2}+mn$
(9)$7{a}^{2}-5{a}^{2}-2{a}^{2}-2ab-ab+{b}^{2}-{b}^{2}=-3ab$
(10)$7ab-7ab-3{a}^{2}{b}^{2}+3{a}^{2}{b}^{2}+8a{b}^{2}-5a{b}^{2}+7-3=3a{b}^{2}+4$
(2)$xy+7xy-5xy=3xy$
(3)$-5a+7a-2b+9b=2a+7b$
(4)$2x-5x-7y+11y-1=-3x+4y-1$
(5)$-3a+2a+2ab-4ab=-a-2ab$
(6)$4{a}^{2}-2{a}^{2}+3{b}^{2}+4{b}^{2}+2ab-ab=2{a}^{2}+7{b}^{2}+ab$
(7)$\frac{1}{2}{m}^{2}+\frac{1}{2}{m}^{2}-3m{n}^{2}+5m{n}^{2}+4{n}^{2}-4{n}^{2}={m}^{2}+2m{n}^{2}$
(8)$-5{m}^{2}n+6{m}^{2}n+4m{n}^{2}-2mn+3mn={m}^{2}n+4m{n}^{2}+mn$
(9)$7{a}^{2}-5{a}^{2}-2{a}^{2}-2ab-ab+{b}^{2}-{b}^{2}=-3ab$
(10)$7ab-7ab-3{a}^{2}{b}^{2}+3{a}^{2}{b}^{2}+8a{b}^{2}-5a{b}^{2}+7-3=3a{b}^{2}+4$