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# C2 edexcel log question Watch

1. help i cant answer this at all
2. What is 3 written as a base 2 logarithm? Then combine the logs on the right hand side and rewrite the log on the left hand side. You should end up with something like:

And then you can say that A=B.
3. (Original post by Tishax2)

help i cant answer this at all

Now use the rule,
4. (Original post by raheem94)

Now use the rule,
what do i do from there ?
5. (Original post by notnek)
What is 3 written as a base 2 logarithm? Then combine the logs on the right hand side and rewrite the log on the left hand side. You should end up with something like:

And then you can say that A=B.

3 is jsut a number

and y >0
6. (Original post by Tishax2)
3 is jsut a number

and y >0
3 is just a number and so is which is equal to 3 (y>0 doesn't change this).

So you have:

Can you follow the next steps in my last post?

Also, it's a good idea for you to try both methods that have been given to you in this thread so you can decide which one you are more comfortable with.
7. 2log2 y - log2 y+6 =3
2log2 y/(y+6) =3
log 2 (y/(y+6)squared = 3
2 cubed = (y/(y+6)) squared.. the rest u should be able to work out
8. (Original post by aeyurttaser13)
2log2 y - log2 y+6 =3
2log2 y/(y+6) =3
log 2 (y/(y+6)squared = 3
2 cubed = (y/(y+6)) squared.. the rest u should be able to work out
You've made a mistake in your second line although it's hard to know for sure because your working isn't clear.

You cannot combine two logs which have different coefficients. In general,

9. (Original post by notnek)
3 is just a number and so is which is equal to 3 (y>0 doesn't change this).

So you have:

Can you follow the next steps in my last post?

Also, it's a good idea for you to try both methods that have been given to you in this thread so you can decide which one you are more comfortable with.
im sorry i really do not understand your method

and especically why you put 3 as a power when it says 3+...

thanks
10. (Original post by Tishax2)
what do i do from there ?

Now use the rule,

You will get a quadratic so you will obtain 2 solutions, reject the value which is less than zero.
11. (Original post by Tishax2)
im sorry i really do not understand your method

and especically why you put 3 as a power when it says 3+...

thanks
Remember,
12. (Original post by Tishax2)
im sorry i really do not understand your method

and especically why you put 3 as a power when it says 3+...

thanks
No problem. I'll try to explain it further.

What I have done is say that 3 is equal to . In your first lessons on logarithms, you should have learnt why this is true. Put into your calculator to convince yourself if you're still not sure.

Remember, etc.

Next I have just replaced 3 with , since they are the same thing.
13. (Original post by notnek)
You've made a mistake in your second line although it's hard to know for sure because your working isn't clear.

You cannot combine two logs which have different coefficients. In general,

oops, ib math exam tmrw and still stupid mistakes! ughh thx for pointing it out its like a warning before my exam tmrw that i gotta DOUBLE CHECK haha
shouldve been log_c a squared - log_c b = log_c a (squared) / b
14. (Original post by raheem94)

Now use the rule,

You will get a quadratic so you will obtain 2 solutions, reject the value which is less than zero.
how do i get the quad equation from here :s
15. (Original post by notnek)
No problem. I'll try to explain it further.

What I have done is say that 3 is equal to . In your first lessons on logarithms, you should have learnt why this is true. Put into your calculator to convince yourself if you're still not sure.

Remember, etc.

Next I have just replaced 3 with , since they are the same thing.
thanks but we did not learn that in class :s
16. (Original post by Tishax2)
how do i get the quad equation from here :s
y^2 / (y+6) = 2^3

y^2 / (y+6) = 8

y^2 = 8(y+6)

y^2 = 8y + 48

y^2 - 8y - 48 = 0

And solve.
17. (Original post by Tishax2)
how do i get the quad equation from here :s

If this confuses you then what's happening is similar to e.g this:

(5 is an arbitrary number that I picked out of the air to show you an example)

Do you understand this? If not, you may need to revise some basic logarithms work.
18. (Original post by Tishax2)
how do i get the quad equation from here :s
19. (Original post by raheem94)

Now use the rule,

You will get a quadratic so you will obtain 2 solutions, reject the value which is less than zero.
i did it and i got y=12
20. (Original post by raheem94)
y=12

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