f(x)=√3sinxcosx +cos²x+ a=√3/2 sin2x+(cos2x+1)/2+a =√3/2 sin2x+cos2x/2+1/2+a=sin(2x+π/6)+aT=2π/2=π 2kπ+π/2<=x+π/6<=2kπ+3π/2 2kπ+π/3<= x <=2kπ+4π/3
