问题
填空题
-a2+2a2=______;如果m-n=50,则5-m+n=______;2ab+b2+______=3ab-b2.
答案
-a2+2a2=(-1+2)a2=a2;
∵m-n=50,∴5-m+n=5-(m-n)=5-50=-45;
∵(3ab-b2)-(2ab+b2)═3ab-b2-2ab-b2=ab-2b2,
∴2ab+b2+ab-2b2=3ab-b2.
故答案为:a2;-45;ab-2b2