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

Reply 40

LL2018

13

Original post by Notnek

No just the 2018 papers but they're locked.

Ah, okay, thanks for your help :smile:

Reply 41

MclarenP1

9

Original post by LL2018

Ah, okay, thanks for your help :smile:

try bilal ahmed blog u'll get thepaper

Reply 42

username3694440

15

In this paper: http://pmt.physicsandmathstutor.com/download/Maths/A-level/C3/Papers-Solomon/for-Edexcel/Solomon%20D%20MS%20-%20C3%20Edexcel.pdf

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

Question 7b, how do you know that x<1/2 ?

Thank you!

Reply 43

username2312801

18

Original post by MclarenP1

try bilal ahmed blog u'll get thepaper

You are legit a lifesaver thank you so much :h:

Reply 44

MayoJack

12

Original post by hello2906

In this paper: http://pmt.physicsandmathstutor.com/download/Maths/A-level/C3/Papers-Solomon/for-Edexcel/Solomon%20D%20MS%20-%20C3%20Edexcel.pdf

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

Question 7b, how do you know that x<1/2 ?

Thank you!

Because in that part, you're solving for the part of the equation and the solution where the modulus is in effect. This only happens at values of x less than 1/2, as over that and that part of the line isn't being modified by the modulus.

Reply 45

username3944682

6

https://www.examsolutions.net/tutorials/examples-using-inverse-trigonometric-functions/?level=A-Level&board=Edexcel&module=C3&topic=1406

I don't remember learning this in class, and I can't see it on the spec - do we need to know how to do this?

Reply 46

Notnek

OP

21

Original post by P1NNumber

https://www.examsolutions.net/tutorials/examples-using-inverse-trigonometric-functions/?level=A-Level&board=Edexcel&module=C3&topic=1406

I don't remember learning this in class, and I can't see it on the spec - do we need to know how to do this?

Questions on inverse trig functions are rare but there's no reason why one won't come up - it's definitely on the spec. The first set of question in that link are unlikely to come up because you can just use your calculator.

Reply 47

Notnek

OP

21

Original post by P1NNumber

How does long division help find the range?

If you use long division you get a quotient of 1 and a remainder of 3 which gives you

1+\frac{3}{x-3}

This may help you find the range because now you could sketch this function by a combination of tranformations. Also in this form it's easier to spot what's happening to the function as x change. I'm not saying you have to split up the fraction like this but it helps some people.

And how do we know ff(x) = x means ff(x) = f^-1(x) or is it just a given?

An inverse function reverses the output of the function. E.g. if you input 3 into

f

and get 4 then if you put 4 into

f^{-1}

you'll get 3.

So

ff(x) = x

means that you're putting x through f and then f again and getting your original value. The only way this can happen is if

f

is equal to

f^{-1}

And is g^-1g(x) always the same as gg^-1(x)?

Yes.

Sorry last minute panic questions, functions haven't been my best :frown:

That's what this thread is here for :smile:

Reply 48

UncookedYogurt

6

Original post by nisha.sri

How do you differentiate y=x^2 lnx / 3 -2x+4
I am having trouble doing x^2lnx/3

Its a product rule, differential of x^2 is 2x and lnx is 1/x, the third is a constant

Reply 49

LL2018

13

Original post by MclarenP1

try bilal ahmed blog u'll get thepaper

Thanks

Reply 50

mathsnerd49

8

Idk if anyone is on to help but on the edexcel june 2017 paper question 3c says you only get the last mark if you've put 7+root21 over 2 not the negative version... why is that? from what i can tell 7-root21 over 2 is also within the conditions so how do you know to only put one of these?

Reply 51

rexs2000

13

does anyone have any tips on how to check over answers i always make silly mistakes and end up losing a few marks

Reply 52

HumzaAhmed

10

Original post by mathsnerd49

Idk if anyone is on to help but on the edexcel june 2017 paper question 3c says you only get the last mark if you've put 7+root21 over 2 not the negative version... why is that? from what i can tell 7-root21 over 2 is also within the conditions so how do you know to only put one of these?

I got confused on this question also. they both seem to meet the condition of being greater than -2.

Reply 53

LL2018

13

Original post by MclarenP1

try bilal ahmed blog u'll get thepaper

Is it only C34 available? I can't find the C3 paper

Reply 54

Notnek

OP

21

Original post by mathsnerd49

Idk if anyone is on to help but on the edexcel june 2017 paper question 3c says you only get the last mark if you've put 7+root21 over 2 not the negative version... why is that? from what i can tell 7-root21 over 2 is also within the conditions so how do you know to only put one of these?

When you square an equation like you will have done in the working of this question, you often generate extra solutions that are invalid. So you always have to check whether they satisfy the original equation. If you try plugging (7-root21)/2 into the equation you'll see that it isn't a solution.

A simpler example : x=1 has one solution, namely x=1. But if you square it you get x^2=1 which has two solutions.

Reply 55

HumzaAhmed

10

Original post by Notnek

When you square an equation like you will have done in the working of this question, you often generate extra solutions that are invalid. So you always have to check whether they satisfy the original equation. If you try plugging (7-root21)/2 into the equation you'll see that it isn't a solution.

A simpler example : x=1 has one solution, namely x=1. But if you square it you get x^2=1 which has two solutions.

I understand the idea that it generates two solutions and one solution is usually the correct one.

but the decimal value of (7-root21)/2 is around 1.2

decimal value of (7+root21)2 is around 5.7

both values > -2 and the domain for g(x) is x > -2. This is why I am confused