∫(π/4-->π/3) cos³x dx
= ∫(π/4-->π/3) cos²x · cosxdx
= ∫(π/4-->π/3) (1 - sin²x) d(sinx)
= (sinx - 1/3 · sin³x) |(π/4-->π/3)
= [sin(π/3) - 1/3 · sin³(π/3)] - [sin(π/4) - 1/3 · sin³(π/4)]
= (√3/2 - 1/3 · 3√3/8) - (√2/2 - 1/3 · √2/4)
= (9√3 - 10√2)/24
≈ 0.06
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