Question: sum/difference property of trig. formula

Hi all,

 

> f := sin(3*t-5);

                              f := sin(3 t - 5)
> expand(sin(x-b));

                        sin(x) cos(b) - cos(x) sin(b)
> f1 := subs({x = 3*t, y = 5}, f);

                             f1 := sin(3 t - 5)
> expand(f);

                      2                                  3                  
4 cos(5) sin(t) cos(t)  - cos(5) sin(t) - 4 sin(5) cos(t)  + 3 sin(5) cos(t)

 

You understand that I want the second form that I have when I use sin(x-b).

Mario

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