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# Stuck on last part of trig identity question. watch

1. secA(sin2A-1)2/[cosA(sec2A - tan2A)]+(2sin2A + cos2A) = 2

secA(sin2A-1)2 = cos3A
[cosA(sec2A - tan2A)] = cosA

what do I do with
(2sin2A + cos2A) ???

and I am new to student room and how do I write equations in a form like other people do?
2. (Original post by Chairm)
secA(sin2A-1)2 / [cosA(sec2A - tan2A)] + (2sin2A + cos2A) = 2

secA(sin2A-1)2 = cos3A
[cosA(sec2A - tan2A)] = cosA

what do I do with
(2sin2A + cos2A) ???

and I am new to student room and how do I write equations in a form like other people do?
You need to use tex. There is a link but essentially, you surround an equation by [] brackets containing tex to open and /tex to close.

Your opener is (in latex) \frac{\secA(\sin2A-1)^2}{[ \cos A (\sec A - \tan 2A)]+(2 \sin 2A + \cos 2A)}=2
Here it with the tex tags on

3. (Original post by Chairm)
secA(sin2A-1)2 / [cosA(sec2A - tan2A)] + (2sin2A + cos2A) = 2

secA(sin2A-1)2 = cos3A

Where did you get this from? It's completely wrong.

Do you know how to expand brackets of the form ?

and I am new to student room and how do I write equations in a form like other people do?
You haven't replied to the other thread that I answered your question on, why not? You can use if you want to typeset equations, but you really need not.
4. (Original post by Zacken)
Where did you get this from? It's completely wrong.

Do you know how to expand brackets of the form ?

You haven't replied to the other thread that I answered your question on, why not? You can use if you want to typeset equations, but you really need not.
oh sorry. I forgotten to put powers.
It's a question given from lesson as a hand out, it doesn't have answer sheet so I cannot check if I am going right way.
tried using latex but it seems a bit difficult...I'll need to look into it more

Oh and for previous post, I have worked out the question and got the answer. Thank you
5. (Original post by Chairm)
oh sorry. I forgotten to put powers.
It's a question given from lesson as a hand out, it doesn't have answer sheet so I cannot check if I am going right way.
tried using latex but it seems a bit difficult...I'll need to look into it more
Not sure I understand, post your corrected working so we can have a look?

Feel free to post your workings using picture, etc... so we can verify them for you if you want. You can make as many threads as you like.

There's no point using LaTex if you're not comfortable with it. Don't worry about it.

Oh and for previous post, I have worked out the question and got the answer. Thank you
It's common courtesy to reply back to the person (SeanFM in this case) who helped you on the thread itself.
6. (Original post by Zacken)
Not sure I understand, post your corrected working so we can have a look?

Feel free to post your workings using picture, etc... so we can verify them for you if you want. You can make as many threads as you like.

There's no point using LaTex if you're not comfortable with it. Don't worry about it.

It's common courtesy to reply back to the person (SeanFM in this case) who helped you on the thread itself.
I've double checked that question. I have corrected the powers. Does it still seem to be wrong?

And yes I am sorry about that. I will do that from now on. I am just not familiar with this forum yet
7. (Original post by Chairm)
secA(sin2A-1)2/[cosA(sec2A - tan2A)]+(2sin2A + cos2A) = 2

secA(sin2A-1)2 = cos3A
[cosA(sec2A - tan2A)] = cosA

what do I do with
(2sin2A + cos2A) ???
So you now have:

So:

Can you think of a familiar trigonometric identity that connects and ?
8. (Original post by Zacken)
So you now have:

So:

Can you think of a familiar trigonometric identity that connects and ?

For this one, how do you get

wouldn't it be

cos^3 A / cosA + (2sin^2A + cos^2A)

and then

cos2A / 2sin2A + cos2A
9. (Original post by Chairm)

For this one, how do you get

wouldn't it be

cos^3 A / cosA + (2sin^2A + cos^2A)

and then

cos2A / 2sin2A + cos2A
The (2 sin^2 A + cos^2 A) aren't in the denominator.

It's
10. (Original post by Zacken)
The (2 sin^2 A + cos^2 A) aren't in the denominator.

It's

oh wow... thought (2 sin^2 A + cos^2 A) was in the denominator the whole time..

Then yes, you are right

2sin^2A +cos^2A + cos^2A = 2sin^2A+2cos^2A

using sin^2A + cos^2A = 1 identity

you get 2...

Thank you so much for your help...
If you didn't correct me that the second part is not in the denominator, I would have never found that suspicious..
11. (Original post by Chairm)
...
No problem. Glad to help.

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