cosαcosβ = 1/2 [ cos(α+β) + cos(α - β) ]
cosx cos2x cos3x
= 1/2 ( cos3x + cosx ) cos3x
= 1/2 cos²(3x) + 1/2 cosx cos3x
= 1/4 ( 1 + cos6x ) + 1/4 ( cos4x + cos2x )
∴ ∫ cosx cos2x cos3x dx
= x/4 + 1/24 sin6x + 1/16 sin4x + 1/8 sin2x +C
追问大神、膜拜••••
追答那就采纳啊
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