等差数列[an]的公差d包含于(0,1),且sin^2*a3-sin^2*a7/sin(a3+a7)
问题描述：
等差数列[an]的公差d包含于(0,1),且sin^2*a3-sin^2*a7/sin(a3+a7)
答
sin²a3=（1/2)(1-cos2a3)sin²a7=(1/2)(1-cos2a7)sin(a3+a7)=sin2a5于是cos2a7-cos2a3=-2sin2a52sin（a7+a3)sin(a7-a3)=-2sin2a5【和差化积】sin4d=-1,0＜d＜1于是d=π/4s10最小,于是a10≤0且a11≥0a1+9d≤...