（1）m+n-p=a(a+b)+(2a-b)^2-(2a-b)(a+2b)=a(a+b)+(2a-b)(2a-b-a-2b)=a(a+b)+(2a-b)(a-3b)=a^2+ab+2a^2-7ab+3b^2=3a^2-6ab+3b^2（2）m+n-p=3a^2-6ab+3b^2=3(a^2-2ab+b^2)=3(a-b)^2