Challenge your maths skills...
Express sin13θ in the form
Asinθ + Bsin^3θ + Csin^5θ +Dsin^7θ + Esin^9θ +Fsin11^θ + Gsin^13θ
A to G being natural numbers.
Basically it's a sum, and the limits on the sum are your counter.
So here, .
So k will go between 0 and .
The is a term in Pascal's triangle.
It might help if you did some research on summation (sigma) notation and Pascal's Triangle.
Summation - Wikipedia, the free encyclopedia
Pascal's triangle - Wikipedia, the free encyclopedia
Now it comes to your question , since you are still unable to catch with it , I will give you an example along with the step numbers**
Put n = 3 and accordingly k =1 so it becomes
Expand the terms
Now gather the values of each term
Add First and second term
Put this in the Step 2 which had those two terms
Thus we have expressed sin(3x) in terms of
**Tell the step number you didn't get
-All you need to do is do the same way for sin(13x) find k, expand,find term values and go ahead