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# Trig question

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1. Trig question
Is Cosec^2(2x) - Cot^2(2x) = 1

Does the double angle thing affect the identity ??
2. Re: Trig question
(Original post by muh123)
Is Cosec^2(2x) - Cot^2(2x) = 1

Does the double angle thing affect the identity ??
The double angle shouldn't affect the identity,

is same as, , where
3. Re: Trig question
(Original post by raheem94)
The double angle shouldn't affect the identity,

is same as, , where
Would it still be the same if it was 2 theta aswell ?
4. Re: Trig question
(Original post by muh123)
Would it still be the same if it was 2 theta aswell ?
Yes.

Now insert

You could have written it as,

Still the answer would be same.
5. Re: Trig question
(Original post by raheem94)
Yes.

Now insert

You could have written it as,

Still the answer would be same.
I was most impressed by your response to other questions but when you substituted a number to "prove" this, I was a little surprised.

It's never possible to prove by numbers. Instead, use algebra!
6. Re: Trig question
(Original post by reallytired)
I was most impressed by your response to other questions but when you substituted a number to "prove" this, I was a little surprised.

It's never possible to prove by numbers. Instead, use algebra!
The OP was stuck at a simple concept, so it was easier to prove him by numbers rather than prove.
Last edited by raheem94; 06-04-2012 at 13:23.
7. Re: Trig question
(Original post by raheem94)
The OP was stuck at a simple concept, so it was easier to DEMONSTRATE TO him by numbers rather than algebra.
rather than prove
8. Re: Trig question
(Original post by TenOfThem)
rather than prove
Thanks for correcting.
9. Re: Trig question
(Original post by raheem94)
Thanks for correcting.
No problem ... after all ... your Post 2 showed the statement to be true for any substitution
10. Re: Trig question
(Original post by TenOfThem)
No problem ... after all ... your Post 2 showed the statement to be true for any substitution
I don't understand why reallytired disagreed with my posts, any reason?

Was it wrong to try to explain by using numbers, i thought it will be easier for the OP to understand in this way.
11. Re: Trig question
By using numbers you only showed that the rule would work for theta=15 rather than a general proof

Given the level of understanding of the OP this would, imo, have been enough to show him that it would work

Reallytired seems to think a proof was required rather than a demonstration ... I guess that he was making the point that in a question that asks you to show or prove using a value to demonstrate would not be enough
Last edited by TenOfThem; 06-04-2012 at 13:54.
12. Re: Trig question
(Original post by reallytired)
I was most impressed by your response to other questions but when you substituted a number to "prove" this, I was a little surprised.

It's never possible to prove by numbers. Instead, use algebra!
(Original post by muh123)
Is Cosec^2(2x) - Cot^2(2x) = 1

Does the double angle thing affect the identity ??
Here is the proof.

,

From the identity,

So,
Last edited by raheem94; 07-04-2012 at 02:39.
13. Re: Trig question
(Original post by raheem94)
Here is the proof.

,

From the identity,

So,
Well done (apart from a slight typo)! You intend to read maths at uni (I recall reading somewhere you are doing A-Levels ATM)?
Last edited by reallytired; 07-04-2012 at 01:54.
14. Re: Trig question
(Original post by reallytired)
Well done! You intend to read maths at uni (I recall reading somewhere you are doing A-Levels ATM)?
No, i am going to do chemical engineering at uni.

If you want to know more about the subjects i am doing, have a look at my profile.
15. Re: Trig question
(Original post by reallytired)
Well done (apart from a slight typo)! You intend to read maths at uni (I recall reading somewhere you are doing A-Levels ATM)?
Thanks for telling me about the typo, i have now corrected it.
16. Re: Trig question
Yeah I knew how to do the proof sorry I was just being really lazy. I was just getting confused because I was thinking to much but many thanks to Raheem94 who cleared it up. it was like 3 in the morning and I was trying to do maths It doesn't work when I'm tired LOL
17. Re: Trig question
(Original post by muh123)
Yeah I knew how to do the proof sorry I was just being really lazy. I was just getting confused because I was thinking to much but many thanks to Raheem94 who cleared it up. it was like 3 in the morning and I was trying to do maths It doesn't work when I'm tired LOL
No problem but time isn't an excuse, i haven't slept from the last 23hours!

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Last updated: April 8, 2012
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