All I only need to see one of the formulas derived step by step. I understand how to derive product-to-sum but have no clue how to do sum-to-product.
Thanks in advance
Hello, viciouspoultry!
I don't remember the derivation, so I came up with one.
It's rather clumsy, but it's valid.
All I only need to see one of the formulas derived step by step.
Consider: . .[1]
Consider: . .[2]
Multiply [1] and [2]: .
. .
. .
. .
We have: .
. . . . . . . .
Multiply by 2: .