5a-2b+3b-4a-1,其中a=-1,b=2 3a²-ab+7-5ab+4a²-7 先化简,再求值 -4a+2b+(5a-b)不求值,要化简

解1题：原式=5a-2b+3b-4a-1=(5a-4a)+(-2b+3b)-1=a+b-1当a=-1,b=2时原式=-1+2-1=0解2题：原式=3a²-ab+7-5ab+4a²-7=(3a²+4a²)+(-ab-5ab)+(7-7)=7a²-6ab当a=-1,b=2时原式=7×(-1)²-6×(-...