Arun
Last Activity: 6 Years ago
Numerator Part
cos 3a + 2 cos 5a + cos 7a = 2 cos 5a cos 2a + 2 cos 5a
Denominator Part
cos a + 2 cos 3a + cos 5a = 2 cos 3a cos 2a + 2 cos 3a
Now
it becomes
2 cos 5a (1 + cos 2a) / 2 cos 3a (1 + cos 2a) = cos 5a / cos 3a
= cos (3a + 2a) / cos 3a
= cos 3a cos 2a / cos 3a – sin3a sin 2a / cos 3a
= cos 2a – sin2a tan 3a
hope it helps
Regards
Arun (askIITians forum expert)
