求函数y=cos^2 x-4cosx x∈[5π/6,7π/6]的值域

问题描述:

求函数y=cos^2 x-4cosx x∈[5π/6,7π/6]的值域

x∈[5π/6,7π/6]
cosx ∈[-1,-√3/2]
y=cos^2 x-4cosx
=cos^2 x-4cosx+4-4
=(cosx-2)^2-4
19/4+2√3