已知:A=3a的平方-4ab,B=a的平方+2ab.(1)求A-2B; (2)若|a+1|+(2-b)=0,求A-2B的值;
问题描述:
已知:A=3a的平方-4ab,B=a的平方+2ab.(1)求A-2B; (2)若|a+1|+(2-b)=0,求A-2B的值;
答
A=3a²-4abB=a²+2ab(1)A-2B=3a²-4ab-2(a²+2ab)=3a²-4ab-2a²-4ab=a²-8ab(2)当|a+1|+(2-b)=0即:a=-1,b=2∴A-2B=(-1)²-8×(-1)×2=1+16=17