合并同类项：（1）½mn-4mn+3mn(2)a³-2a²+3a-6-4a³+2a²+2a+2

合并同类项：（1）½mn-4mn+3mn(2)a³-2a²+3a-6-4a³+2a²+2a+2
合并同类项：（1）½mn-4mn+3mn(2)a³-2a²+3a-6-4a³+2a²+2a+2

合并同类项：（1）½mn-4mn+3mn(2)a³-2a²+3a-6-4a³+2a²+2a+2
（1）½mn-4mn+3mn=½mn-mn=-½mn
(2) a³-2a²+3a-6-4a³+2a²+2a+2
=a³-4a³-2a²+2a²+3a+2a-6+2
=-3a³+5a-4