Why are equations written in double angle form?

[EastWindBreaks]

Homework Statement

I guess this is a general question. in the book, it was originally in a normal form, but it was then converted into a double angle form, which I would have to use double angle formula to compute, so what's the point of simplifying in the first place?

Homework Equations

The Attempt at a Solution

 

[scottdave]

I guess it depends on what your unknown quantities are. The formulae in the gray box are much simpler, so there is less opportunity to make a mistake. That would be one advantage. Also, if it is something that you are memorizing, it is less to memorize, rather than all of those sin(theta)cos(theta) etc, for example.

 

[EastWindBreaks]

I guess it depends on what your unknown quantities are. The formulae in the gray box are much simpler, so there is less opportunity to make a mistake. That would be one advantage. Also, if it is something that you are memorizing, it is less to memorize, rather than all of those sin(theta)cos(theta) etc, for example.

I guess you are right, its more compact, easier to remember.