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## godorovg 2 years ago Okay here is the deal, I am studying to test out of two math classes, I need someone to show step by step how to Sum of products in trig and Cos laws I have problems this not a the test. i am only studying. I will be attending IU east on-line this summer studying math. Please show me how to do it not give me answers only thanks.

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1. godorovg

here is the problem cos6x+cos2x=0

2. godorovg

sin2xcos2x-cos2x=0

3. inkyvoyd

two tips that are meant as general self study guidelines: sign up for a free account on wolfram alpha, and use step-by-step solution after entering equations. Use resources such as Khan Academy, Purple Math (I believe), Wikipedia, and SOS math (I believe). I think paul's online math notes has good info too. Note that I have given you 7ish names and no links - trust me, these worked for me, especially the first, if you do not have openstudy to help you. Good luck, and have fun!

4. calmat01

Youtube also has some good math videos. Just type in sum and difference trig identity and you should find what you are you looking for.

5. godorovg

I know you plug in for this I am just not how?

6. godorovg

so we use this form in cosucosv=1/2{cosu-v)+cos(u+v0} so now we plug in?

7. calmat01

Cos u+Cos v =2Cos((u+v)/2)Cos((u-v)/2)

8. calmat01

So now just make the appropriate substitutions for u and v.

9. godorovg

when plugging in for U and v does the 1/2 mean a power?

10. calmat01

No, it's multiplying the sum and difference of the two angles by 1/2.

11. godorovg

cosucosv=1/2 cos 6x+cos2x=0

12. godorovg

is this right so far?

13. calmat01

Actually, it should be 2cos4xcos2x=0

14. godorovg

okay that is what I need help with?

15. godorovg

1/2 of 6 is only 3??

16. calmat01

Sum of 6x and 2x is 8x divided by 2 is 4x. Difference of 6x and 2x is 4x divided by 2 is 2x.

17. calmat01

You do not take halfe of each angle you take half of their sum and then half of their difference.

18. godorovg

so you add 6+2= 8 and than divide the sums by 2?

19. calmat01

Yes, and then you do it again only use their difference.

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