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Edexcel A2 C3 Mathematics 12th June 2015

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Original post by samb1234
Firstly you don't really need to know a whole lot, as most are either on the formula sheet or can easily be derived from it eg sin2a isn't on there but sin(a+b) is so you can just do sin(a+a) to get the identity for sin2a. The only ones you really have to know are 1+tan^2 =sec^2 and 1+cot^2 =cosec^2

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Awesome thanks for that.. ok this is probably gonna be a really dumb question but I after putting sina+a I got sinAcosA + cosAsinA .. is that the same as 2(sinAcosA) cause one of them is the other way round *hides face*
Original post by pearl_rose
Awesome thanks for that.. ok this is probably gonna be a really dumb question but I after putting sina+a I got sinAcosA + cosAsinA .. is that the same as 2(sinAcosA) cause one of them is the other way round *hides face*


Yes its the same just like (3x2) +(2x3) is the same as (3x2) + (3x2)

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Reply 702
Avatar for Rkai01
Rkai01
6
Is the quotient rule:
VU' - UV' / VSQUARED
Original post by Rkai01
Is the quotient rule:
VU' - UV' / VSQUARED


Yes it is. And anyway its on the formula sheet

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Original post by randlemcmurphy
For "1+tan^2 =sec^2 and 1+cot^2 =cosec^2" I would just recommend remembering sin2x+cos2x=1, and then altering that in the exam for the specific identity needed.


Original post by samb1234
Yes it is fairly easy to derive that one as well (just divide by sin^2 or cos^2) I just put that one as a lot of people don't realise that there is even an identity linking them so may not realise to do that in the exam

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Oh ok thanks guys, what about the Rsin(x+a) types? And how do you get to 1+tan^2=sec^2 and 1+cot^2=cosec^2 from sin2x+cos2x=1?
Original post by Rkai01
Is the quotient rule:
VU' - UV' / VSQUARED


Not sure, but it is in the formula booklet.
Original post by pearl_rose
Oh ok thanks guys, what about the Rsin(x+a) types? And how do you get to 1+tan^2=sec^2 and 1+cot^2=cosec^2 from sin2x+cos2x=1?


For Rsin(x+a) I would expand it to get Rsinxcosa+Rcosxsina and then equate terms.

For 1+tan^2=sec^2 divide sin2x+cos2x=1 by cosine.
For 1+cot^2=cosec^2 divide sin2x+cos2x=1 by sine.
Reply 707
Avatar for Rkai01
Rkai01
6
And D/Dx (SechX) = -SechXTanhX right?
Original post by pearl_rose
Oh ok thanks guys, what about the Rsin(x+a) types? And how do you get to 1+tan^2=sec^2 and 1+cot^2=cosec^2 from sin2x+cos2x=1?


Rsin(x+a) expand sin(x+a) and do coefficient matching eg if you had 7sinx + 4cosx then when you expand rsin(x+a) you would get Rsinxcosa +rsinacosx. By matching the coefficients of the two, you can say that rcosa =7 and rsina=4. Then you can divide the two to get tan a. R is basically coefficient if sin squared plus coefficient of cos squared all rooted. For us it normally tells you its positive but just be careful as it could be -ve. To get the two identities you just divide by either sin^2 or cos^2

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Original post by Rkai01
And D/Dx (SechX) = -SechXTanhX right?


Fp3

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Reply 710
Avatar for Rkai01
Rkai01
6
Do we have to set up rates of change differentiating Q's?
Original post by randlemcmurphy
Not sure, but it is in the formula booklet.


Is it the f(x)/g(x) one? We have to learn the product and chain rule off by heart though right?
Original post by pearl_rose
Is it the f(x)/g(x) one? We have to learn the product and chain rule off by heart though right?


Product and chain rule you need to know yes but they are fairly easy to remember

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Original post by samb1234
Product and chain rule you need to know yes but they are fairly easy to remember

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Ok, thanks so much :]
Reply 714
Avatar for Rkai01
Rkai01
6
Also what's the chances of being asked to sketch a sec cos or cot graphs?
For the Rsin(x + a) thing is it ok (ie will I get full marks) if I just remember how to do it straight away without working (eg for the above you do a = arctan (coefficient of cos over coefficient of sin)

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Original post by aersh8
For the Rsin(x + a) thing is it ok (ie will I get full marks) if I just remember how to do it straight away without working (eg for the above you do a = arctan (coefficient of cos over coefficient of sin)

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You would risk losing marks. No point in doing that really not like it takes long to write it out (especially if you made a stupid mistake you would get 0)

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Original post by samb1234
Rsin(x+a) expand sin(x+a) and do coefficient matching eg if you had 7sinx + 4cosx then when you expand rsin(x+a) you would get Rsinxcosa +rsinacosx. By matching the coefficients of the two, you can say that rcosa =7 and rsina=4. Then you can divide the two to get tan a. R is basically coefficient if sin squared plus coefficient of cos squared all rooted. For us it normally tells you its positive but just be careful as it could be -ve. To get the two identities you just divide by either sin^2 or cos^2

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Original post by randlemcmurphy
For Rsin(x+a) I would expand it to get Rsinxcosa+Rcosxsina and then equate terms.

For 1+tan^2=sec^2 divide sin2x+cos2x=1 by cosine.
For 1+cot^2=cosec^2 divide sin2x+cos2x=1 by sine.


Ok how are y'all moving from rsin(x+a) to Rsinxcosa + Rcosxsina?
Original post by pearl_rose
Ok how are y'all moving from rsin(x+a) to Rsinxcosa + Rcosxsina?


Expansion of sin(x+a)

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Original post by samb1234
Expansion of sin(x+a)

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I don't follow :[

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