Question

cosxcosy=1/2(sin(x+y)+sin(x-y))
True or False

Answer 1

@tkhunny

Answer 2

Have you considered first multiplying by 2 and then expanding the two sine arguments?

Answer 3

yea

Answer 4

and so I came to true, but not sure?

Answer 5

Did you do any part of it incorrectly on purpose? If not, then I must ask, "Why do you doubt?"

Answer 6

I really don't know?

Answer 7

Well, that's a horrible way to live. You'll have to show me your work before I can bless it. Expand those sines and let's see how you did what you did.

Answer 8

I wrote it on paper, but I now belief its true.

Answer 9

Seriously? You have no confidence unless I demand to see your work, then suddenly it becomes good work? This makes no sense. Why not gain confidence in your work?

Answer 10

I tend to overthink every single thing I do

Answer 11

That's not necessarily a bad thing. You just have to learn to control it. If you learn the notation well enough to write clearly and accurately, you should be able to follow what you did and check your work. Don't be afraid to write the whole thing over again while you take very small, easily-reproduced steps.

Answer 12

So then this would also be true according to me an^2 x = 1-cos2x/ 1+ cos2x

Answer 13

Please post new question on new threads. It looks to me as if you have not written this correctly, so it is not likely to be verified as "true". You probably meant, tan^2 x = (1-cos2x)/(1+ cos2x). The parentheses are NOT optional. You need to know why.

Answer 14

Thank you!