已知函数f(x)=2cos2x+sin平方x-4cosx

f(x)=2cos2x+sin^x-4cosx
=2(2cos^x-1)+(1-cos^x)-4cosx
=3cos^x-4cosx-1
f(π/3)=3cos^(π/3)-4cosπ/3-1=3x(1/2)^-4x1/2-1=(-9)/4;
令t=cosx,t∈[-1,1].F(t)=3(t^2)-4t-1
F'(t)=6t-4 令F'(t)=0,t=2/3;
t∈[-1,2/3],F(t)递减,t∈[2/3,1],F(t)递增.
f(x)(min)=F(2/3)=(-7)/3;
F(-1)=6,F(1)=-2,f(x)(max)=max{F(-1),F(1)}=6;