Question

Just check my answer?!!! Will medal!!

Verify the identity.

cos (x - y) - cos (x + y) = 2 sin x sin y

Answer 1

trig identities for sum and difference:
cos (a + b) = cos a cos b - sin a sin b
cos (a - b) = cos a cos b + sin a sin b

cos (x - y) - cos (x + y) =
cos x cos y + sin x sin y - (cos x cos y - sin x sin y) =
cos x cos y + sin x sin y - cos x cos y + sin x sin y =
2 sin x sin y

Answer 2

@Kkutie7

Answer 3

So this last step here, you did what?
`cos x cos y + sin x sin y - cos x cos y + sin x sin y`
You just combined like-terms?

Answer 4

seems good :)

Answer 5

So should I change anything? @zepdrix

Answer 6

nah, seems perfect

Answer 7

Thanks so much!!