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# A-level Maths help core 4 trig identites watch

1. struggling at the moment with proving trig identities and doing the integration parts, does anyone have any advice on how to approach these kinds of questions
2. (Original post by students1999)
struggling at the moment with proving trig identities and doing the integration parts, does anyone have any advice on how to approach these kinds of questions
Remember trig identities. Practice.
3. (Original post by students1999)
struggling at the moment with proving trig identities and doing the integration parts, does anyone have any advice on how to approach these kinds of questions
With the trig identities all you need to do is remember the standard cos^2(x) + sin^2(x) = 1 and then when you want to derive the others you can just divide both sides by sin^2(x) or by cos^2(x). I did this at the start of every C4 paper at the top of my page so that I had them as a reference during the exam
Also some people in my school found that a helpful way to remember which functions are involved is using the phrases:
cosy cottage (cosec^2(x) = 1 + cot^2(x))
sexy tan ( sec^2(x) = 1 + tan^2(x))

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4. (Original post by stepmaths)
With the trig identities all you need to do is remember the standard cos^2(x) + sin^2(x) = 1 and then when you want to derive the others you can just divide both sides by sin^2(x) or by cos^2(x). I did this at the start of every C4 paper at the top of my page so that I had them as a reference during the exam
Also some people in my school found that a helpful way to remember which functions are involved is using the phrases:
cosy cottage (cosec^2(x) = 1 + cot^2(x))
sexy tan ( sec^2(x) = 1 + tan^2(x))

Posted from TSR Mobile
This is a good method for students who don't know the identities before the exam. But for students targeting the top grades it's really useful for them to know the identities off by heart.

Sometimes questions won't refer to an identity directly and only students who are very familiar with an identity would recognise what to do. An example: one year there was an exam question which involved the fraction

Students who knew the identity by heart noticed that the denominator could be written as and so the fraction is equal to . This change allowed them to progress with the question. Students who weren't as familiar with the identity were much less likely to recognise this.

Some students become very familiar with the identies after doing loads of practice question. For others, it's a good idea to spend 30 mins one day learning them e.g. look at them then try to write them out and repeat until you can write them without looking. It really doesn't take long to learn them.
5. (Original post by stepmaths)
With the trig identities all you need to do is remember the standard cos^2(x) + sin^2(x) = 1 and then when you want to derive the others you can just divide both sides by sin^2(x) or by cos^2(x). I did this at the start of every C4 paper at the top of my page so that I had them as a reference during the exam
Also some people in my school found that a helpful way to remember which functions are involved is using the phrases:
cosy cottage (cosec^2(x) = 1 + cot^2(x))
sexy tan ( sec^2(x) = 1 + tan^2(x))

Posted from TSR Mobile
thank you for the advice im revising maths now and will give it a go and thanks for the phrases dont think i will be forgetting them anymore hahaha
6. (Original post by notnek)
This is a good method for students who don't know the identities before the exam. But for students targeting the top grades it's really useful for them to know the identities off by heart.

Sometimes questions won't refer to an identity directly and only students who are very familiar with an identity would recognise what to do. An example: one year there was an exam question which involved the fraction

Students who knew the identity by heart noticed that the denominator could be written as and so the fraction is equal to . This change allowed them to progress with the question. Students who weren't as familiar with the identity were much less likely to recognise this.

Some students become very familiar with the identies after doing loads of practice question. For others, it's a good idea to spend 30 mins one day learning them e.g. look at them then try to write them out and repeat until you can write them without looking. It really doesn't take long to learn them.
thank you for this, dont think i would of got that question either tbh and i definately will be learning the identities off by heart
7. 2[1/2sinxcosx] = 2 . 1/sin2x which when it integrates become 2/sin2x then ln|sin2x| + C where C = 2c.
Because 2 . 1/2 is the same as saying 1.

Or if you get 2cosec2x it integrates to -cosec2xcot2x + C which I think may be the correct answer if it is saying about trig identities in the question.

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