∫(π/6→π/2)cos²xdx
=∫(π/6→π/2)(1+cos2x)/2dx
=∫(π/6→π/2)1/2dx+1/2 ∫(π/6→π/2)cos2xdx
=1/2(π/2-π/6)+1/4∫(π/6→π/2)dsin2x
=π/6+1/4sin2x(π/6→π/2)
=π/6+1/4(0-√3/2)
=π/6-√3/8