proving trig identities

[scenic rapids]

i am not comprehending of the process

[runic nebula]

what is task

[scenic rapids]

oh i posted it in the wrong place so i deleted

[runic nebula]

seems eveything legit u just wrote on bottom right sin((x-y)/2)

should be cos((x-y)/2) instead

[scenic rapids]

oh i see

[runic nebula]

but well done

[scenic rapids]

its my teachers solution haha

[runic nebula]

oh now i get it so u had questions to it?

[scenic rapids]

i was wondering why A and B are added and subtracted where it says a+b a-b

[runic nebula]

Apparently the approach seems to be to use the following identities:

So we can define the arguments of the RS

$\A := \frac{x+y}{2}\$

$\B := \frac{x-y}{2}\$

[tired prairie]

adonhs

[runic nebula]

Since we are using the identities we can calculate A + B and A - B

which gives us (no coincidence) A + B = x and A - B = y

So it follows:

$\ cos(x) + cos(y) = cos(A+B) + cos(A-B)\$

now we can use the identity theorems

[tired prairie]

adonhs

[runic nebula]

And when evaluating we end up with what we wanted to prove in the beginning

[scenic rapids]

ohhhhhhhhh

okk ic ic thank u

[runic nebula]

If there are no questions anymore u may close the case with .solved

[scenic rapids]

.solved