You are Here: Home >< Maths

# Harder C2 Logs watch

1. Anyone doing Edexcel knows how much a pain the mixed exercise is for the log chapter. The book goes over the very basics i.e the rules and nothing else. Are there any sites/ tutorials on how to use logs for harder questions like in this exercise. Some examples include using simultaneous equations to work out certain values when given two expressions (one as logs, one as exponentials).
2. just do past paper questions
3. That's the thing, I need a resource to tell me how to work them out as I'm not sure. The book doesn't say much and then it goes straight into hard questions with no background.
4. Don't just do past papers as you may get one that they haven't done before.

http://schools.spsd.sk.ca/mountroyal/hoffman/

The section 'mathb30' has a load in with some notes or you can just watch youtube.

past papers are useless if hyou dont know ALL the rules
5. The mixed exercise in the Heinemann book did have a few hard ones, but they can all be done using the standard log rules you practised in the previous exercises.

If you have any specific questions, post them + your working/thoughts.
6. Seriously, don't do the mixed exercise ones.
7. (Original post by ViralRiver)
x
I've done C2, and I used this book. It was brilliant:
http://www.amazon.co.uk/Level-Mathem...5222704&sr=8-6
But even better than that book is actual past paper questions. You can't go wrong when you practise with actual exam questions.

8. (Original post by ViralRiver)
Anyone doing Edexcel knows how much a pain the mixed exercise is for the log chapter. The book goes over the very basics i.e the rules and nothing else. Are there any sites/ tutorials on how to use logs for harder questions like in this exercise. Some examples include using simultaneous equations to work out certain values when given two expressions (one as logs, one as exponentials).
I agree with you OP the whole chapter is easy but the mixed exercise is completely differnet. I would suggest using the Cd and going to the hint section and looking over previous questions. If you are stuck follow through the bit where it shows you step by step.

Btw they are questions from previous questions
9. (Original post by Swayum)
The mixed exercise in the Heinemann book did have a few hard ones, but they can all be done using the standard log rules you practised in the previous exercises.

If you have any specific questions, post them + your working/thoughts.
Well I am completely stuck with this one. Not sure what to do.

8y = 42x + 3
log2y = log2x + 4
10. (Original post by ViralRiver)
Well I am completely stuck with this one. Not sure what to do.

8y = 42x + 3
log2y = log2x + 4
lol, exactly what im doing atm brah. My skool being cheap and not even giving me the CD, *******s, CD would give me a play a play of the steps. i swear, i should take a dump on Mr.O's Honda
11. (Original post by Narik)
I've done C2, and I used this book. It was brilliant:
http://www.amazon.co.uk/Level-Mathem...5222704&sr=8-6
But even better than that book is actual past paper questions. You can't go wrong when you practise with actual exam questions.

does it contain an interactive CD?
12. Any help?
13. I remember doing this last year.
It was a complete waste because none of the questions in the exams were even remotely as hard as the mixed excercise ones.
14. Unfortunately it's homework so I've got to do the entire exercise. I don't see me doing too well if I'm stuck on question 6 --" .
15. (Original post by ViralRiver)
Well I am completely stuck with this one. Not sure what to do.

8y = 42x + 3
log2y = log2x + 4
Ok, so when you first start out at C2, you kind of just take logs base 10 mainly, yeah? So let's try it and see what happens (when I write log, I mean log base 10):

log(8^y) = log(4^(2x + 3))

Ok, now I look at it and think "Aha! There's a power there, let's hit with the power rule even though I don't really know where it's going, but I don't care"

ylog8 = (2x+3)log4

So y = (2x + 3)(log4)/log8

Now I look at the second equation and realise that I want to take logy to base 2. But my expression above is already too messy, so I'll start again:

This time I stare at the equations and think about why my previous approach failed. It failed because the second equation had log to base 2, where as I took log to base 10. So why don't I start off by taking log to base 2? If I use the notation log(2, x) to mean log(x) base 2, then:

8^y = 4^(2x + 3)

So log(2, 8^y) = log(2, 4^(2x + 3))

So again, I use my power rule as before and find

ylog(2,8) = (2x+3)log(2,4)

But hang on, log(2,8) = 3 and log(2,4) = 2 surely?

So 3y = 2(2x+ 3) = 4x + 6

This is looking promising. But what about the second equation? If I can remove all logs, it'll boil down to a year 8 simultaneous equations problem, right? So let's try it:

log(2,y) = log(2,x) + 4

I want to get rid of all logs somehow. I have two logs, my first move should be to reduce it to just one log. Do I know any way of doing that? Of course I do:

log(2, y) - log(2, x) = 4

So log(2, y/x) = 4

And then, using the definition of logs, y/x = 2^4 = 16

So y = 16x

And now it's very easy because I already know 3y = 4x + 6 from above. This gives me a solution.

But then I look back and wonder if there was a faster way. Of course there was:

8^y = 4^(2x + 3)

(2^3)^y = (2^2)^(2x + 3) because 8 = 2^3 and 4 = 2^2

But C1 tells me that this is just

2^(3y) = 2^(4x + 6)

Now if you stare at that long enough, you can see that the only way it can be true is if 3y = 4x + 6. The equation is just saying that 2^something = 2^something_else, so something = something_else. If I say 2^x = 2^9, then x = 9, right? Likewise here.
16. are you sure it needs to be that hard??????
17. yeah, that whole exercise is damn hard.

but believe me guys, once you crack it, please be assured that you will be able to solve any log question that you may be given in C2
18. Thanks, Swayum. However, I was able to complete the question after re-reading it over and over again, in a simpler way than you described, I believe. Unfortunately I'm stuck with the question after it xD - but I'm just going to keep re-reading it.
19. (Original post by ViralRiver)
Thanks, Swayum. However, I was able to complete the question after re-reading it over and over again, in a simpler way than you described, I believe. Unfortunately I'm stuck with the question after it xD - but I'm just going to keep re-reading it.
Post this question and why it's bothering you, somebody will be able to help.
20. (Original post by ViralRiver)
Thanks, Swayum. However, I was able to complete the question after re-reading it over and over again, in a simpler way than you described, I believe. Unfortunately I'm stuck with the question after it xD - but I'm just going to keep re-reading it.
What's the next question?

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: February 6, 2010
The home of Results and Clearing

### 1,749

people online now

### 1,567,000

students helped last year
Today on TSR

### University open days

1. Sheffield Hallam University
Tue, 21 Aug '18
2. Bournemouth University
Wed, 22 Aug '18
3. University of Buckingham
Thu, 23 Aug '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams