题目

等差数列{an}中,an≠0,n∈N*,有2a3-a72+2a11=0,数列{bn}是等比数列,且b7=a7,则b6b8等于A.2                   B.4                   C.8                 D.16 答案：D  等差数列{an}中,a3+a11=2a7,∴4a7-a72=0.∴a7=4.∴b6·b8=b72=a72=16.在△ABC中，∠ABC和∠ACB的平分线相交于点I． (1)若∠A=50°，则∠BIC=________°； (2)若∠BIC=110°，则∠A=________°．