Question

cos 130 cos 40 - sin 130sin 40=cos 90
can someone tell me if this is correct?

Answer 1

Correct.

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

cos(130-40) = cos 130 cos 40 - sin 130 sin 40
cos (90) = cos 130 cos 40 - sin 130 sin 40

Answer 2

yay! thank you!!!!!!

do you have time for one more if you can check it for me?