Trig sum formulas

[ImAnEngineer]

sin(a + b) = sin(a)cos(b) + cos(a)sin(b)
sin(a - b) = sin(a)cos(b) - cos(a)sin(b)

cos(a + b) = cos(a)cos(b) - sin(a)sin(b)
cos(a - b) = cos(a)cos(b) + sin(a)sin(b)

Who first derived them? When, and how?

Thanks

 

[tiny-tim]

Who first derived them? When, and how?

Not how, but Howe … Julia Ward Howe, in 1861, derived them, and they became a Civil War marching song, to the tune now known as the Battle Hymn of the Republic.

 

[ImAnEngineer]

Not how, but Howe … Julia Ward Howe, in 1861, derived them, and they became a Civil War marching song, to the tune now known as the Battle Hymn of the Republic.

If it's a joke... sorry but I don't get it.

 

[tiny-tim]

If it's a joke... sorry but I don't get it.

try singing it!

 

[ImAnEngineer]

try singing it!

Struggling to get a nice melody... :P

Any serious comments?