Quandaries and Queries
Who is asking: Student
sin A + sin B = 2sin(A+B/2)cos(A-B/2)
cos A - cos B = -2sin(A+B/2)sin(A-B/2)
cos A + cos B = 2cos(A+B/2)cos(A-B/2)
sin A - sin B = 2cos(A+B/2)sin(A+B/2)
Please help im almost there with these babies and it's very frustrating!
I will illustrate how to derive the first expression. To do it I am going to assume that you know that
From these I can derive
Adding equation 1 and equation 2 I get
If you now let P = A + B/2 and Q = A - B/2 you will se that this is exactly the expression in your first problem.
The other can be derived in a similar fashion.