;;;2.(多选)(2020新高考Ⅰ,11,5分,中)已知a0,b0,且a+b=1,则?(????)

A.a2+b2≥?????B.2a-b?????

C.log2a+log2b≥-2????D.?+?≤?;解析????

由a0,b0,a+b=1,得?≥?=?,即a2+b2≥?,当且仅当a=b=?时取等号,故A正

确;

由a0,b0,a+b=1,得a-b=2a-1-1,故2a-b?,故B正确;

log2a+log2b=log2(ab)≤log2?=log2?=-2,当且仅当a=b=?时,等号成立,故C错误;

(?+?)2=a+b+2?=1+2?≤1+