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# Logs Watch

1. (Original post by dongonaeatu)
dont understand the second step
I have used the change of base law in order to make both of the bases the same so I can then combine the logs into one single log.

The change of base law is as follows:

logax = logbx/logba

^ Learn that formula.

log2x + log4x = 2

a = 4
b = 2

So it turned into:

log2x + log2x/log24 = 2
2. (Original post by Joshmeid)
log2x + log4x = 2

log2x + log2x/log24 = 2

log2x + log2x/2 = 2

2log2x + log2x = 4

3log2x = 4

log2x^3 = 4

x^3 = 16

x = 2.52(3sf)

Ask if you are confused by anything.
Please don't post full solutions, they are considered a last resort.
3. (Original post by Joshmeid)
I have used the change of base law in order to make both of the bases the same so I can then combine the logs into one single log.

The change of base law is as follows:

logax = logbx/logba

^ Learn that formula.

log2x + log4x = 2

a = 4
b = 2

So it turned into:

log2x + log2x/log24 = 2
thanks i go it
4. (Original post by avtar95)
could u put that in letters
According to the change of base rule can be written as

In the question it was
So here

Lets use the change of base rule, we want the base of logs to be 2 hence let

Do you get it?
5. (Original post by raheem94)
According to the change of base rule can be written as

In the question it was
So here

Lets use the change of base rule, we want the base of logs to be 2 hence let

Do you get it?
kinda its quite complicated though
6. (Original post by dongonaeatu)
is that rule just for log2x and log4x i've never been taught that
Remember

So cannot be written in that way as both have different bases.
7. (Original post by raheem94)
Please don't post full solutions, they are considered a last resort.
thanks i go it
8. (Original post by dongonaeatu)
kinda its quite complicated though
It isn't complicated with a bit of practice you will be fine with it.
9. (Original post by raheem94)
Remember

So cannot be written in that way as both have different bases.
are the bases the a's so the number in front of the log
10. (Original post by dongonaeatu)
are the bases the a's so the number in front of the log
The a's are the bases.
11. (Original post by raheem94)
It isn't complicated with a bit of practice you will be fine with it.
so loga 5 +loga 4= loga20 as the base is the same (a)

but loga5+ logb4= not log20 as different bases what would i do in this instance
12. (Original post by dongonaeatu)
so loga 5 +loga 4= loga20 as the base is the same (a)

but loga5+ logb4= not log20 as different bases what would i do in this instance
Yes,

And

For solving such questions you need to put both on the same base. Lets change the base of to

So now the equation becomes,
You can see that now all the logarithms have the same base.

Do i make any sense?
13. (Original post by raheem94)
Yes,

And

For solving such questions you need to put both on the same base. Lets change the base of to

So now the equation becomes,
You can see that now all the logarithms have the same base.

Do i make any sense?
did u use the change of base loga^b=logc to the b/logc to the a

and u make C the base ur changing it to
14. (Original post by dongonaeatu)
did u use the change of base loga^b=logc to the b/logc to the a

and u make C the base ur changing it to
I am not understanding your question.

I used the change of base rule to convert to
15. (Original post by raheem94)
I am not understanding your question.

I used the change of base rule to convert to
do i have to learn the change of base formula

and the C in the equation is the log of what u are converting it to so if i want it in base of a i have the C as a
16. (Original post by dongonaeatu)
do i have to learn the change of base formula

and the C in the equation is the log of what u are converting it to so if i want it in base of a i have the C as a
Yes, you have to learn the change of base formula.

And yes the C in my equation is 'a', and your concept about this is correct. I wanted the log to have the base 'a' hence i set 'C' to 'a'.
17. (Original post by raheem94)
Yes, you have to learn the change of base formula.

And yes the C in my equation is 'a', and your concept about this is correct. I wanted the log to have the base 'a' hence i set 'C' to 'a'.
do i get given the formula in the exam and how many hours of maths do u do a day u are amazing
18. (Original post by dongonaeatu)
do i get given the formula in the exam and how many hours of maths do u do a day u are amazing
I don't know if the formula will be given or not, but this is a simple formula. Just understand it, don't try to mug it up.

I have already finished A-Level maths(C1-4, M1-2), with an A* , now i am doing further maths, so C2 is simple for me. I don't work too much, A-Level maths isn't hard. Just go through the chapters in the book and you will be fine with it. Try to understand things, do you use a book?
19. (Original post by raheem94)
I don't know if the formula will be given or not, but this is a simple formula. Just understand it, don't try to mug it up.

I have already finished A-Level maths(C1-4, M1-2), with an A* , now i am doing further maths, so C2 is simple for me. I don't work too much, A-Level maths isn't hard. Just go through the chapters in the book and you will be fine with it. Try to understand things, do you use a book?
wow A* thats great well done. i have a green edxcel textbook and a c2 resource pack and access to past papers and marked solutions
20. (Original post by dongonaeatu)
wow A* thats great well done. i have a green edxcel textbook and a c2 resource pack and access to past papers and marked solutions
I also used the green edexcel text books, they are great. I self-studied all units using them, they explain really well. Have you read the chapters properly?

Updated: February 8, 2016
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