cos²θ/2-sin²θ/2=cosθ
所以(a-1)cosθ=a+1
cosθ=(a+1)/(a-1)
θ是三角形的最小内角
所以0<θ<=60度
1/2<=cosθ<1
1/2<=(a+1)/(a-1)
(a+1)/(a-1)-1/2>=0
(2a+2-a+1)/(a-1)>=0
所以(a+3)(a-1)>=0
a<=-3,a>1
(a+1)/(a-1)<1
(a+1)/(a-1)-1<0
2/(a-1)<0
a<1
所以a<=-3
转载请注明原文地址:https://54852.com/read/592093.html
