Prove that cos3a+2cos5a+cos7a/cos a +2cos3a+ cos5a equals to cos2a-sin2atan3a
Mayank Gupta , 5 Years ago
Grade 11
Trigonometry> Prove that cos3a+2cos5a+cos7a/cos a +2cos...
1 Answers
Arun
Last Activity: 5 Years ago
Dear student
cos3A+2cos5A+cos7A)/(cosA+2cos3A+cos5A)
= 2cos 5A [cos 2A + 1] / 2cos 3A [cos 2A + 1]
= cos 5A / cos 3A
= [cos 3A cos 2A -- sin 3A sin 2A] /cos 3A
= cos 2A -- sin 2A tan 3A
= 2cos 5A [cos 2A + 1] / 2cos 3A [cos 2A + 1]
= cos 5A / cos 3A
= [cos 3A cos 2A -- sin 3A sin 2A] /cos 3A
= cos 2A -- sin 2A tan 3A
Regards
Arun
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