Question

Prove that cos 3a + 2 cos 5a + cos 7a ? cos a + 2 cos 3a+ cos 5a = cos 2a - sin 2a tan 3a

Answer 1

(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

$\huge\pink{brainliest\:plz}$

Answer 2

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