cos 35 cos 85 cos 155=?
sumanth , 9 Years ago
Grade 12th pass
Trigonometry> cos 35 cos 85 cos 155=?
1 Answers
Lab Bhattacharjee
Last Activity: 9 Years ago
cos(155)=cos(180-25)=-cos(25)
So, cos35 cos85 cos155 =-cos25 cos(60-25)cos(60+25)
Now prove 4cosx cos(60-x) cos(60+x)=cos3x
cos75=cos(45+30)=...
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