- 高一数学计算题a取何值时不等式a^2+2a
- a取何值时不等式a^2+2a-sin^x-2ac>2的解集是实数集R
- a^2+2a-sin^x-2acosx>2
a^2+2a-1+cos^x-2acosx>2
cos^x-2acosx+a^2+2a-3>0
令cosx=t,
t^2-2at+a^2+2a-3>0
对称轴为t=a
当定义域是R时，-1<=t<=1
1.a<-1
f(-1)>0
a<-2-√6
2.-1<=a<=1
Δ<=0
-1<=a<=1
3.a>1
f(1)>0
a>2
综上：a<-2-√6 or -1<=a<=1 or a>2