Sum to Product and Product to Sum Identities

just print them out if you really need them

I don't know anyone who has these memorized

>>9000497
>I already remember the addition of angles formulas like sin(a+b)=sin(a)cos(b)+cos(a)sin(b)
Yes, just add those formulas.

>>9000497
that fourth equation is redundant, it follows from the third

>>9000498
on an exam?

>>9000497
Just write them as complex exponentials and re-derive them as needed.

>>9000509
yea......I meant easier and not time consuming. I want hacks like the "magic hexagon" for trig functions type of shit.

>>9000515
Not everything has an easy way.

>>9000523
Well for poor people...(unlucky for me).

>>9000515
Dude, they are obvious if you know the addition identities.
You want cosa cosb ?
Well, in which identities does cos a cos b appear?
In cos(a+b) and cos(a-b):

cos(a+b) = cosa cosb - sina sinb
cos(a-b) = cosa cosb + sina sinb

Add the equations and get

cos(a+b) + cos(a-b) = 2 cosa cosb

that's it

>>9000526
>>9000515
how is exponential notation time consuming? the derivation to each expression is a couple lines at most.. that's as taxing as

>>9000570 is.

also you pump up those work shown bullshit points if you're doing this for an exam.