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# C3 Trig question Watch

1. Solve 8cotX - 3tanX = 2

I need help with the re-arranging

8 1/TanX - 3 tanX = 2

do I divide by tan?
2. (Original post by Jonario)
Solve 8cotX - 3tanX = 2

I need help with the re-arranging

8 1/TanX - 3 tanX = 2

do I divide by tan?
Try multiplying by tanx on both sides and rearrange a little, do you notice anything? Perhaps a substitution...?
3. (Original post by zcomputer5)
Try multiplying by tanx on both sides and rearrange a little, do you notice anything? Perhaps a substitution...?
Ahh that just made it worse, I'm confused now D:

8(1/tan^2X) - 3tan^2X = 2Tan

Has this got something to do with the double angle formulae?
4. (Original post by Jonario)
Ahh that just made it worse, I'm confused now D:

8(1/tan^2X) - 3tan^2X = 2Tan

Has this got something to do with the double angle formulae?
This is just an example but what is 2X(1/2)?
Now tell me what is AX(1/A)?
Now what is (Tanx)x(1/tanx)?
5. If you multiply by tanx, it just turns into a simple quadratic. Just call tanx, u and maybe that'll make more sense.

Where in the world did you get 2x from?
6. (Original post by zcomputer5)
This is just an example but what is 2X(1/2)?
Now tell me what is AX(1/A)?
Now what is (Tanx)x(1/tanx)?
Is that relevant to the question? I'm totally confused now soz
7. (Original post by Jonario)
Is that relevant to the question? I'm totally confused now soz
Well he's basically saying that:

8. (Original post by StephenP91)
If you multiply by tanx, it just turns into a simple quadratic. Just call tanx, u and maybe that'll make more sense.

Where in the world did you get 2x from?
Tan to the power of 2 X ?

So when I multiply by Tan i'll get

8(1/tan^2 X ) - 3 tan^2 X = 2tan?
9. (Original post by StephenP91)
If you multiply by tanx, it just turns into a simple quadratic. Just call tanx, u and maybe that'll make more sense.

Where in the world did you get 2x from?
I was trying to help him rather than just giving him the answer as if you read his last post you would of realise that he made a mistake multipling both sides through by tanx. Therefore I can him some example for him i.e. 1/2 X 2 =1!
10. (Original post by StephenP91)
Well he's basically saying that:

Oh my apologies, I didn't visualise it like that.
11. (Original post by Jonario)
Tan to the power of 2 X ?

So when I multiply by Tan i'll get

8(1/tan^2 X ) - 3 tan^2 X = 2tan?
You get 8 -3 tan^2 X = 2tanx
12. (Original post by zcomputer5)
You get 8 -3 tan^2 X = 2tanx
Yep :P

then I rearrange to get

3Tan^2X = 6 ?

Then I square root the 6 and find tan^-1 ?
13. (Original post by zcomputer5)
This is just an example but what is 2X(1/2)?
Now tell me what is AX(1/A)?
Now what is (Tanx)x(1/tanx)?
you're making him confused!
14. (Original post by Jonario)
Yep :P

then I rearrange to get

3Tan^2X = 6 ?

Then I square root the 6 and find tan^-1 ?
You've gone wrong. You end up with a quadratic equation. Let me show you.

Multiply by Tanx

Simply re-arrange.

Quadratic equation. You can either make a substitution to make it look like quadratics you've previously dealt with or simply factorise as it is. Makes no difference.
15. (Original post by Jonario)
Yep :P

then I rearrange to get

3Tan^2X = 6 ?

Then I square root the 6 and find tan^-1 ?
Since when did 8-2tanx=6?

No, to solve the quadratic its easiest to make a substitution, i.e. let Tanx=u to get
3u^2 +2u -8=0 perhaps you can solve it from here?
16. (Original post by Jonario)
Solve 8cotX - 3tanX = 2

I need help with the re-arranging

8 1/TanX - 3 tanX = 2

do I divide by tan?

tANX(8/TAnx - 3 tanx)= 2tan x

8-3tan^2(x)=2tanx

3tan^2(x)+2tanx - 8 = 0

and you solve the rest
17. (Original post by TobeTheHero)
you're making him confused!
Well I thought that All A-level mathematians should be able to compute those fractions, I am pretty sure I learnt them for key stage 3 at school?
18. (3tanx-4)(tanx+2)=0

19. (Original post by zcomputer5)
Since when did 8-2tanx=6?

No, to solve the quadratic its easiest to make a substitution, i.e. let Tanx=u to get
3u^2 +2u -8=0 perhaps you can solve it from here?
I got (3t-4)(t+2)

so tanX = 4/3, tan X= -2

correct?

Thanks guys
20. (Original post by Jonario)
I got (3t-4)(t+2)

so tanX = 4/3, tan X= -2

correct?

Thanks guys
well done! you could always do it without using substitution

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