1.设等差数列{an}满足:[sin^2(a3)-cos^2(a3)+cos^2(a3)*cos^2(a6)-sin^2
1.设等差数列{an}满足:[sin^2(a3)-cos^2(a3)+cos^2(a3)*cos^2(a6)-sin^2(a3)*sin^2(a6)]/sin(a4+a5)=1,公差d∈(-1,0).若当且仅当n=9时,数列{an}的前n项和Sn取得最大值,则首项a1的取值范围是()
A.(7π/6,4π/3) B.(4π/3,3π/2) C.[7π/6,4π/3] D.[4π/3,3π/2]
2.在△ABC中,角A、B、C的对边分别是a、b、c,则a>b是cosA