求函数y=cosx*[cosx-cos(x+2/3)]的最值高一水平有关三角函数性质的

求函数y=cosx*[cosx-cos(x+2/3)]的最值高一水平有关三角函数性质的
求函数y=cosx*[cosx-cos(x+2/3)]的最值
高一水平有关三角函数性质的

求函数y=cosx*[cosx-cos(x+2/3)]的最值高一水平有关三角函数性质的
y=cosx*(-2)sin[(x+x+2/3)/2]sin[(-2/3)/2]
=2cosxsin(x+1/3)sin(1/3)
=2sin(1/3)cosxsin(x+1/3)
= 2sin(1/3)(1/2)*[sin(2x+1/3)+sin(1/3)]
=sin(1/3)sin(2x+1/3)+sin^2(1/3).
ymax=sin^2(1/3)+sin(1/3);
ymin=sin^(1/3)-sin(1/3).