;;;2.(2017山东,7,5分,中)若ab0,且ab=1,则下列不等式成立的是?(????)

A.a+??log2(a+b)B.?log2(a+b)a+?

C.a+?log2(a+b)?D.log2(a+b)a+??;3.(2018课标Ⅲ理,12,5分,难)设a=log0.20.3,b=log20.3,则?(????)

A.a+bab0????B.aba+b0

C.a+b0ab????D.ab0a+b;考点2不等式的解法;解析????

解法一:利用“数轴标根法”求解

因为ab≠0,所以a≠0且b≠0,设f(x)=(x-a)(x-b)(x-2a-b),则f(x)的零