∫(π/6→π/4) cos2x dx
= (1/2)sin2x
= (1/2)[sin(2 · π/4) - sin(2 · π/6)]
= (1/2)[sin(π/2) - sin(π/3)]
= (1 - √3/2)/2
= 1/2 - √3/4
∫(π/6→π/4) cos2x dx
= (1/2)sin2x
= (1/2)[sin(2 · π/4) - sin(2 · π/6)]
= (1/2)[sin(π/2) - sin(π/3)]
= (1 - √3/2)/2
= 1/2 - √3/4