f:= Sin[x]+Cos[x]+2*Cos[2.2*x]

Plot[f,{x,0,6}]

g:= D[f,x]

FindRoot[g==0,{x,0,1}]

f /. %

FindRoot[g==0,{x,1,2}]

f /. %

FindRoot[g==0,{x,2,3}]

f /. %

FindRoot[g==0,{x,4,5}]

f /. %

FindRoot[g==0,{x,5,6}]

f /. %