若，且． （1）求的最小值及对应的x值； （2）若不等式的解集记为A，不等式的解...

20．(1) ∵ ∴ ，∴ ∴ a = 2或a = 1（舍）····································································· 2分 又 ∵ ∴        ∴ b = 2······························································· 4分 ∴ ， ∴ 当时，的最小值为······························· 6分 (2) 由 ∴ ∴ ∴ ，即······································· 9分 由 ∴ ∴ ······································································· 11分 ∴ ···································································· 12分 【解析】略