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`intcos 2x cos 4x cos 6xdx`

Answer» `int cos 2x cos 4x cos 6x dx`
`=(1)/(2) int cos 4x(2 cos 6x cos 2x)dx`
`=(1)/(2) int cos 4x(cos 8x + cos 4x)dx`
`=(1)/(4) int(2 cos 8x cos 4x+2 cos^(2)4x)dx`
`=(1)/(4) int (cos 12x+cos 4x+cos 8x+1)dx`
`=(1)/(4)((sin12x)/(12)+(sin 4x)/(4)+(sin8x)/(8)+c)+c`


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