∫(π/6→π/2) cos²x dx
= ∫(π/6→π/2) (1+cos2x)/2 dx
= (x+0.5sin2x)/2 | (π/6→π/2)
= (π/2 - π/6 - 0.5sinπ/3)/2
= π/6 - √3 /8