Thank you for registering.

One of our academic counsellors will contact you within 1 working day.

Please check your email for login details.
MY CART (5)

Use Coupon: CART20 and get 20% off on all online Study Material

ITEM
DETAILS
MRP
DISCOUNT
FINAL PRICE
Total Price: Rs.

There are no items in this cart.
Continue Shopping

This problem is from the trigonometry chapter ` Transformations of sums and products` . I am stuck with this problem. Can anyone pls suggest me how to solve this?

This problem is from the trigonometry chapter ` Transformations of sums and products` . I am stuck with this problem. Can anyone pls suggest me how to solve this?

Question Image
Grade:12th pass

1 Answers

Aditya Gupta
2075 Points
2 years ago
the sum can be written as S=∑1/(cosa+cos(2r+1)a), r being from 1 to n
now , S= ∑1/2cos(r+1)acos(ra)
now, 2S*sina= ∑(sin((r+1)a – ra)/cos(r+1)acos(ra))
=  ∑tan(r+1)a – tanra [using sin(a-b)= sinacosb – sinbcosa]
the above sum telescopes, giving
2S*sina= tan(n+1)a-tana
or S= coseca(tan(n+1)a-tana)/2

Think You Can Provide A Better Answer ?

Provide a better Answer & Earn Cool Goodies See our forum point policy

ASK QUESTION

Get your questions answered by the expert for free