In[]:=
f[x_]:=0.5x^2+Cos[Pix]-2Sin[2Pix]+Cos[3Pix]Sin[Pix]
In[]:=
Minimize[f[x],x]
Out[]=
{-3.0233,{x-0.711232}}
In[]:=
NMinimize[f[x],x]
Out[]=
{-3.0233,{x-0.711232}}