① -3(2x²-xy)-4(x²-xy-6)=-6x²+3xy-4x²+4xy+24=-10x²+7xy+24 ②5a²-[（5a²-2a）-2（a²-3a）]=5a²-(5a²-2a-2a²+6a)=5a²-(3a²+4a)=5a²-3a&...