## Darion Group Title Can someone help me please? Rewrite with only sin x and cos x. cos 2x + sin x one year ago one year ago

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1. Schrodinger Group Title

Okay. So this stems from trigonometric identities and double angle formulas. Do you know any double angle formulas?

2. Darion Group Title

Not really, no. Sorry

3. Schrodinger Group Title

No prolem. A really good reference for all of these formulas would be this: (one minute.)

4. Schrodinger Group Title

*No problem. Anyways, here's the webpage with pretty much every possible identity you can imagine for Trig. http://www.sosmath.com/trig/Trig5/trig5/trig5.html You'll notice that under the double angle formulas section, Cos(2x) has three different accompanying equations. Can I ask what math you're in right now, i'm assuming Precalc?

5. Darion Group Title

You are correct, I'm in precalc. And thanks for the link btw. That is awesome.

6. Schrodinger Group Title

$\cos(2x) = \cos ^{2}(x) - \sin ^{2}(x)$$\cos(2x) = 2\cos ^{2}(x)-1$$\cos(2x) = 1 - 2\sin ^{2}(x)$

7. Schrodinger Group Title

No problem. Okay, given these formulas, we can substitute cos(2x) for other things without double angles. Right now, we've got $\cos(2x) + \sin(x)$, correct?

8. Darion Group Title

Yes

9. Schrodinger Group Title

(Sorry for asking something you obviously know the answer to, just giving myself time to think LOL. I haven't done this in a while.)

10. Darion Group Title

No you're doing great. You're helping me way more than anyone has thus far. Take all the time you need I really appreciate your helping me out man.

11. Schrodinger Group Title

No worries. I'm a little confused about the vague instructions. While you can rewrite it with those terms, i'm wondering if it's acceptable to have only sine, only cosine, or whether cosine or sine squared is acceptable. After all, that is basically what these are. Guess every case might be worked out.

12. Darion Group Title

If it helps, the possible answers are: 1 + 3 sin x 1 + 3 sin2x 1 - 2 sin2x + sin x 1 + 2 sin2x + sin x

13. Darion Group Title

The last 3 are (sin^2 x) btw

14. Schrodinger Group Title

Oh, lol, okay then. That's WAY simpler than what I was about to do. My bad, I was like, half-trying to solve a trig identity. So yeah, just take a look at the formulas I put up, and substitute them. From there it's super easy to see which one makes sense with the possible answers.

15. Schrodinger Group Title

Don't try to solve anything, just see which substitution would get you closest to the answers given. It should be a single step.

16. Schrodinger Group Title

You follow?

17. Darion Group Title

I think so. So the answer would just be 1 - 2 sin2x + sin x

18. Schrodinger Group Title

Exactly, but I have to say, don't be afraid of using the carat symbol (^) if you're ever writing something on a computer and can't put in a fancy superscript like: $\sin ^{2}x$ to denote when a value is squared. People could very, very easily misread it as sin(2x) instead of sin^2(x), and that could mess up a whole problem.

19. Darion Group Title

Thanks for the tip and all your help. I can't thank you enough.

20. Schrodinger Group Title

No problem. Good luck with Precalc. I struggled a lot with it when I first learned it.

21. Schrodinger Group Title

(Heck, i'm still learning it, albeit different forms.)

22. Darion Group Title

Haha. I guess it never really ends does it?

23. Schrodinger Group Title

Nope. We're dumb forever. :P PS, I don't know if this would apply to you, but do you use flash cards to study?

24. Darion Group Title

sometimes. I guess it depends on what I am studying. If there are a lot of vocabulary words or something I will usually use flashcards.