Prove that cos 3a + 2 cos 5a + cos 7a ? cos a + 2 cos 3a+ cos 5a = cos 2a - sin 2a tan 3a
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Answered by
44
(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
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Answered by
12
Answer:
Step-by-step explanation:
(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
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