令cosx^2=t
原式=[6t^2+5(1-t)-4]/(2t-1)
=(6t^2-5t+1)/(2t-1) [6t^2-5t+1=(2t-1)(3t-1)]
=3t-1
=3cosx^2-1
=3cos2x/2+1/2
定义域R 值域[-1,2]
f(x)=f(-x)
偶函数