`int cos x cos 2x cos 3x dx` का मान ज्ञात कीजिए।

Explanation

दिया है - `int cos x cos 2xcos 3x dx`
` = (1)/(2)int(2cos x cos 2x) cos 3x dx`
` = (1)/(2)int (cos 3x + cos x)cos 3x dx`
` = (1)/(2)int(cos^(2) 3x + cos x cos 3x)dx`
` = (1)/(4)int(2cos^(2) 3x)dx+(1)/(4)int(2cos x cos 3x) dx`
` = (1)/(4)int(1+cos 6x )dx +(1)/(4) int(cos 4x + cos 2x)dx`
` =(1)/(4) intdx +(1)/(4) int cos 6x dx = (1)/(4) int cos 6dx +(1)/(4) int cos 4xdx +(1)/(4) int cos 2xdx`
` = (1)/(4) x+(1)/(4).(sin 6x)/(6)+(1)/(4).(sin 4x)/(4) +(1)/(4).(sin 2x)/(2)+c`
` = (x)/(4) +(sin 6x)/(24) +(sin 4x)/(16) +(sin 2x)/(8)+e`