C3 Last Minute Questions Thread (Edexcel 1 day to go!)

OP

Original post by nisha.sri

Also guys when do you use arccos? I was doing a question and it was like -0.586=cos(30t +16.70 ) and they said do use arccos why cant you just do cos^-1 ? Is it because of the negative on the other side ?

arccos(x) and cos^-1(x) are the same thing so I’m confused by your question.

Reply 23

RhiannaTimms

12

Original post by nisha.sri

Also guys when do you use arccos? I was doing a question and it was like -0.586=cos(30t +16.70 ) and they said do use arccos why cant you just do cos^-1 ? Is it because of the negative on the other side ?

Not sure if this is me being dumb but I'm pretty sure arccos and cos^-1 are the same thing.

EDIT: looked this up just to be sure because if I was wrong this would be a problem! Looks like I'm right, they're the same thing, and arccos is just a word used instead of cos^-1 (when cos^-1 is the inverse of cos, NOT cos to the power of -1)

(edited 5 years ago)

Reply 24

bluenotewitt

11

Is differentiation from first principle required? For example, could we be asked to prove that the derivative of the sine function is equal to the cosine function?

Reply 25

username3694440

15

http://pmt.physicsandmathstutor.com/download/Maths/A-level/C3/Papers-Solomon/for-Edexcel/Solomon%20L%20QP%20-%20C3%20Edexcell.pdf

How would you do question 1 without drawing a graph? (I know you could technically draw a graph in this question, but for questions similar to this where you can't draw a graph, what approach do you need to take?)

Reply 26

OP

Original post by hello2906

http://pmt.physicsandmathstutor.com/download/Maths/A-level/C3/Papers-Solomon/for-Edexcel/Solomon%20L%20QP%20-%20C3%20Edexcell.pdf

How would you do question 1 without drawing a graph? (I know you could technically draw a graph in this question, but for questions similar to this where you can't draw a graph, what approach do you need to take?)

The domain is x>2 so first consider values very close to 2. These values will results in the denominator being very close to 0 so the whole fraction will be very big. This shows that there is no upper limit for the range because as x gets closer to 2, the fraction will get bigger and bigger.

Now consider what happens as x gets bigger. The -3 on top and the -2 on bottom become irrelevant so the fraction will get closer and closer to

\dfrac{2x}{x}

and that is equal to 2. So 2 must be the lower boundary on the range.

Alternatively, you can use a division method e.g. long division since this is an improper fraction to end up with

\displaystyle 2+\frac{1}{x-2}

Then it may be easier to find the range or sketch the graph.

(edited 5 years ago)

Reply 27

username2312801

18

You know when you do x1,x2,x3 ... and then sometimes it asks you what is the value for tetha, how would you work that out from the x1,x2,x3 values ? Hope im making sense haha

Reply 28

OP

Original post by nisha.sri

You know when you do x1,x2,x3 ... and then sometimes it asks you what is the value for tetha, how would you work that out from the x1,x2,x3 values ? Hope im making sense haha

I think you'll need to give an example :smile:

Reply 29

username2312801

18

Original post by Notnek

I think you'll need to give an example :smile:

The last bit :smile:

2018-06-18 (2).png58.5KB

Reply 30

OP

Original post by nisha.sri

The last bit :smile:

If you just need to state the value to 3dp then just keep pressing equals on your calculator to get an accurate solution then write it to 3dp. It's only 1 mark so you just need to write an answer.

Often with these questions you have to prove that the value of alpha is something. For cases like this it's best to consider the upper and lower bounds and check that there is a change of sign when you plug them into the original function.

Reply 31

Original post by Notnek

If you just need to state the value to 3dp then just keep pressing equals on your calculator to get an accurate solution then write it to 3dp. It's only 1 mark so you just need to write an answer.

Often with these questions you have to prove that the value of alpha is something. For cases like this it's best to consider the upper and lower bounds and check that there is a change of sign when you plug them into the original function.

Can you please help me with this solomon paper question please? I'm really desperate, I'll attach the question and their answer
c3 question 2.PNG

OP

Original post by LL2018

Can you please help me with this solomon paper question please? I'm really desperate, I'll attach the question and their answer
c3 question 2.PNG

You need to explain where you're stuck.

Reply 33

Original post by Notnek

You need to explain where you're stuck.

For part (i)
1.) I rearranged to get x=e^y
2.) Then I subbed it into log2(x) to get log2(e^y)
3.) Then I rearranged to get (y)log2(e)

But their answer is y/ln2 :frown:

Reply 34

OP

Original post by LL2018

For part (i)
1.) I rearranged to get x=e^y
2.) Then I subbed it into log2(x) to get log2(e^y)
3.) Then I rearranged to get (y)log2(e)

But their answer is y/ln2 :frown:

Your answer is the same as theirs but in a different form so it's fine. The quickest way to do this question is to use the change of base formula (which isn't directly on the spec). The problem with solomon papers is that they sometimes go off the spec. Only do them if you've done all the Edexcel UK papers and IAL papers.

Reply 35

Original post by Notnek

Your answer is the same as theirs but in a different form so it's fine. The quickest way to do this question is to use the change of base formula (which isn't directly on the spec). The problem with solomon papers is that they sometimes go off the spec. Only do them if you've done all the Edexcel UK papers and IAL papers.

Oh oh, I started the solomon papers as I finished all the edexcel ones but I think I'm just going to give this one a miss. Thanks for clearing it up

Reply 36

OP

Original post by LL2018

Oh oh, I started the solomon papers as I finished all the edexcel ones but I think I'm just going to give this one a miss. Thanks for clearing it up

Have you done the IAL papers?

Reply 37

Original post by Notnek

Have you done the IAL papers?

I've only found 2014-2017 IAL papers, are there any more that I'm unaware of?

Reply 38

OP

Original post by LL2018

I've only found 2014-2017 IAL papers, are there any more that I'm unaware of?

No just the 2018 papers but they're locked.

Reply 39

OP