Question

uluio

Answer 1

Use the sum & difference formula for cosine to expand the cos(x-y) and cos(x+y).
I think you can find those in your textbook or online:

Answer 2

can you show me the steps?

Answer 3

Use the formula for sum and difference. Take a look at the attachment. You have cos(x-y). The only difference is taht in the attachment it's cos(u-v), but it's the same thing.
cos(x-y) = cos(x)cos(y) + sin(x)sin(y)
Do the same thing with the second cosine
cos(x+y) = _____________

Then, combine everything using algebra (combine like terms together, meaning add and or subtract and possibly cancel out some terms - HINT) and you will see that it matches nicely.

Answer 4

but I get 2 cos x + 2 cos y+ 2 sin x + 2 sin y
what do i do now?

Answer 5

Are you sure that's what you get? Notice that they are different when you have cos(x-y) and cos(x+y).
They are NOT the same. One is coscos+sinsin and the other is coscos-sinsin

Answer 6

can you work it out because im not understanding