求值域：y=2cos(派/3+x)+2cosx

y = 2cos(π/3+x)+2cosx = 2 {cos(π/3+x)+2cosx }= 2 * 2 cos{π/3+x+x)/2} cos{π/3+x-x)/2}= 4 cos(x+π/6) cos{π/6}= 4 cos(x+π/6) * √3/2= 2√3 cos(x+π/6) cos(x+π/6) ∈【-1,1】y ∈【-2√3 ,2√3】...