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# Edexcel A2 C3 Mathematics 12th June 2015 watch

1. https://07a69ccf283966549a9350d1a669...%20Edexcel.pdf

For 9b, I made a mistake I thought that because it's 3theta that means sin(3theta - 1.1071) = 3 not 1, can someone explain to me?

and for c I thought the min value would be -1 for the sin bit
https://07a69ccf283966549a9350d1a669...%20Edexcel.pdf

For 9b, I made a mistake I thought that because it's 3theta that means sin(3theta - 1.1071) = 3 not 1, can someone explain to me?

and for c I thought the min value would be -1 for the sin bit
Sin has a range of -1 and 1.

For min value questions you usually think 'oh, it's going to be -1', but in the equation H(theta), if your sin function outputs -1, what does H(theta) equal? So is it a minimum? (By sin function outputting one I mean sin(3theta-a) = -1, so that's without R and the other stuff.
3. Hi, could someone help me on this question
"Given that 2 sin(θ + 30)° = cos(θ + 60)°, find the exact value of tan θ °."

2sin(θ + 30)° = cos(θ + 60)°
2sinθ°cos30° + 2cosθ°sin30° = cosθ°cos60° – sinθ° sin60°
2root3/2 sinθ° +2/2cosθ° =1/2 cosθ° – root3/2 sinθ°
Finding tanθ°, tanθ° = – 1/3root3 or equiva.

I don't understand how you get the last bit of the answer, could someone help me please
4. (Original post by Ripper Phoenix)
how do you get range of functions that look like this:

1/(x+1)(x-1) or 2x/(3x+5)

like also how do i know when to say y is not equal to 0 as part of the range answer

help?
One rule of thumb is to compare the leading term of the numerator and your denominator (the term with the highest power of x) and look at the ratio of your coefficients.

So for your first one, it's 1/(x^2-1). When x is large, it becomes 1/a very large number, so it seems to be going to 0. I suspect that you can't have a number a such that 1/a = 0, so y won't be equal to 0. (One way of thinking about it is that because x is large, x^2 is large, so the -1 is of little consequence, so you're left with 1/x^2. If you think about x = 1000, then f(x) = 1/((1000^2)-1), which is probably very close to 1/(1000^2).

If you have 2x/3x+5 and x becomes large, so that +5 becomes of little consequence, what do you think it will converge to?
5. (Original post by mat1996)
Hi, could someone help me on this question
"Given that 2 sin(θ + 30)° = cos(θ + 60)°, find the exact value of tan θ °."

2sin(θ + 30)° = cos(θ + 60)°
2sinθ°cos30° + 2cosθ°sin30° = cosθ°cos60° – sinθ° sin60°
2root3/2 sinθ° +2/2cosθ° =1/2 cosθ° – root3/2 sinθ°
Finding tanθ°, tanθ° = – 1/3root3 or equiva.

I don't understand how you get the last bit of the answer, could someone help me please
equation has been divided by cosθ
6. Do we need to know about counter examples then?
7. For the domain and range sometimes the mark scheme doesn't include x/f(x) is equal to all real numbers. I f you do include it do you loose marks?
8. I am really confused when solving these mod equations; for the 2nd solution, how do you know which side to put the minus on, because I am pretty sure there have been questions where it has been required for it to be put on alternate sides (e.g the minus on the mod equation side, and then on the non-mod side (not on the same question!!))

Sorry if this is confusing, but any help would be really appreciated. If anyone could just talk me through part b, to determine on which side you would put the minus, the question being from the June 2014 (R) paper that would also be much appreciated.

9. (Original post by TeeEm)
equation has been divided by cosθ
OMG, I can't believe i didn't see that. Thank you so much for your help but you know when I do it on the calculator it gives me -root3/9. Would examiners know this is equivalent or should i change it to the other answer (and how would I know this in the exam)
10. (Original post by SeanFM)
Sin has a range of -1 and 1.

For min value questions you usually think 'oh, it's going to be -1', but in the equation H(theta), if your sin function outputs -1, what does H(theta) equal? So is it a minimum? (By sin function outputting one I mean sin(3theta-a) = -1, so that's without R and the other stuff.
ok thanks! so basically even if it's 3theta 4theta or whatever theta sin and cos will always be within -1 to 1 their usual range, got it!
Another thing, I was sketching |8-2x| and got my line extending a bit into the second quadrant but I did the mod bit correct by reflecting what's in the negative x axis above, but in the markscheme they don't have the line extending, so i was wondering if you could explain??
ok thanks! so basically even if it's 3theta 4theta or whatever theta sin and cos will always be within -1 to 1 their usual range, got it!
Another thing, I was sketching |8-2x| and got my line extending a bit into the second quadrant but I did the mod bit correct by reflecting what's in the negative x axis above, but in the markscheme they don't have the line extending, so i was wondering if you could explain??
I'm not 100% sure what you mean, from what points to what points is it extending on your sketch?
12. (Original post by Maham88)
which solomon paper is this from ?
F and L IIRC.
13. Whats the general consensus on Solomon vs Elmwood? Which is harder? I've finished all the Solomon papers so far and have just done the first Elmwood- it seemed easier to me...
14. Is it possible to put something like

3sinx + 2cosx in the form Rsin(x-alpha) ?

Or is it always Rsin(x+alpha) ?

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15. (Original post by SeanFM)
I'm not 100% sure what you mean, from what points to what points is it extending on your sketch?
As in it from the y axis at 8 but the graph in the markscheme just has it start from 8
16. Do we need to know how to solve inequalities involving modulus stuff?

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As in it from the y axis at 8 but the graph in the markscheme just has it start from 8
Ah, so you've got values like 10, 12 in the second quadrant?

If so, it's possible that they specified a domain, or that they're not interested in the bits to the left of the y axis but you probably wouldn't lose marks unless they specified the domain.

(Original post by it's a me, mario)
Is it possible to put something like

3sinx + 2cosx in the form Rsin(x-alpha) ?

Or is it always Rsin(x+alpha) ?

Posted from TSR Mobile
I think it is possible, if it was +alpha and you had it in the form -alpha then alpha would be a negative value.
18. (Original post by TheRaspberry)
I am really confused when solving these mod equations; for the 2nd solution, how do you know which side to put the minus on, because I am pretty sure there have been questions where it has been required for it to be put on alternate sides (e.g the minus on the mod equation side, and then on the non-mod side (not on the same question!!))

Sorry if this is confusing, but any help would be really appreciated. If anyone could just talk me through part b, to determine on which side you would put the minus, the question being from the June 2014 (R) paper that would also be much appreciated.

square both sides and solve for x its easy
19. (Original post by it's a me, mario)
Do we need to know how to solve inequalities involving modulus stuff?

Posted from TSR Mobile
I thought that was in C4
20. (Original post by mat1996)
I thought that was in C4
no its c3

also i have a strong feelin that we may be asked to draw modulus graphs like

y=IX+2I +2 or something like that lol

i'm paranoid

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