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# period of cos x Watch

1. Add 2pi to both of them to get all the solutions.

(Original post by Alen.m)
so basically i've got my first answer as 2pi/3 , substrate this from 2pi will give me the second angle which is 4pi/3 now keep adding 2pi to 2pi/3 or 4pi/3?does it really matter?
2. (Original post by constellarknight)
Add 2pi to both of them to get all the solutions.
does the part you mentioned 2pi-2pi/3=4pi/3 necessary ?
3. yes, the solutions for 5x are 2pi/3 + 2pi, 4pi, etc. AND 4pi/3 + 2pi, 4pi, etc.
4. (Original post by constellarknight)
yes, the solutions for 5x are 2pi/3 + 2pi, 4pi, etc. AND 4pi/3 + 2pi, 4pi, etc.
if the question was based on tan then we should subtract from 180 right?like 180-x
5. No. For tan, it's simpler: get your first solution by taking tan^-1, then just keep adding or subtracting multiples of 180.
6. (Original post by constellarknight)
No. For tan, it's simpler: get your first solution by taking tan^-1, then just keep adding or subtracting multiples of 180.
so the first solution doesn't need to be subtracted from 180 just need to be added by pi,2pi,3pi etc?
7. Yes. But remember, you can subtract pi, 2pi, 3pi, etc. as well as adding them.
8. (Original post by constellarknight)
Yes. But remember, you can subtract pi, 2pi, 3pi, etc. as well as adding them.
does it make a difference if i choose adding than subtracting?
9. You have to do both to get the full range of solutions.
10. (Original post by constellarknight)
You have to do both to get the full range of solutions.
Still abit confusing knowing when to add and when to subtrac, for instance we've only done adding for the question we've been discussing apart from the part that 2pi-2pi/3=4pi/3
11. (Original post by Alen.m)
Still abit confusing knowing when to add and when to subtrac, for instance we've only done adding for the question we've been discussing apart from the part that 2pi-2pi/3=4pi/3
You will need to look at your situation and question and decide there, basically all your answers need to be in the range specified in the question, for some questions you'll only need to add, for others you'll only need to subtract, and for others you'll need to do both. If you're confused. Do both and then throw away all the ones that don't fit in your range.
12. (Original post by Zacken)
You will need to look at your situation and question and decide there, basically all your answers need to be in the range specified in the question, for some questions you'll only need to add, for others you'll only need to subtract, and for others you'll need to do both. If you're confused. Do both and then throw away all the ones that don't fit in your range.
That helped a lot thank you
13. (Original post by Alen.m)
That helped a lot thank you
No problemo, you'll get a hang of it once you practice a few questions, you'll be able to see exactly what you should right away.
14. (Original post by Zacken)
No problemo, you'll get a hang of it once you practice a few questions, you'll be able to see exactly what you should right away.
Yeah i think the key to this problem is practising a few questions, im revising everything on my own so that's why i get stuck at some places

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