已知函数f(x)=2cos2x+sinx的平方-4cosx 求f(兀/3)的值

带入x=π/3
f(x)=2cos2π/3+sinπ/3的平方-4cosπ/3
=2(-cos π/3)+sinπ/3的平方-4cosπ/3
=2(-1/2)+(根号3/2)^2-4*1/2
=-1+3/4-2
=-9/4