'Taking Logs'

Say you 'take logs' of this:

7^{x}=7^{2x}-12

Is the correct result A or B?

A

\log_7 7^{x}=\log_7 7^{2x}-\log_7 12

B

\log_7 7^{x}=\log_7(7^{2x}-12)

The answer is B

Original post by DoubleDoors

Say you 'take logs' of this:

7^{x}=7^{2x}-12

Is the correct result A or B?

A

\log_7 7^{x}=\log_7 7^{2x}-\log_7 12

B

\log_7 7^{x}=\log_7(7^{2x}-12)

B.

If you start with the expression in a, then you can use law of logs (that log(a/b) = loga - logb and then undo the logs to see that you would have 7^x = 7^2x / 12, which is not what you started with.

So the thing to take away is that if you take logs of both sides, it is the log of literally the whole thing rather than the sum of individual logs of each term.

Reply 3

BirdIsWord

17

Im bad at maths but arent A and B the same once you expend B?

Reply 4

Zacken

22

Original post by BirdIsWord

Im bad at maths but arent A and B the same once you expend B?

No, review your logarithm laws. Logarithms are non-linear.

Reply 5

username2250433

13

Why is the base 7? does that matter or have you just used it as an example? so it could be 10 or something else

Reply 6

Zacken

22

Original post by not_lucas1

Why is the base 7? does that matter or have you just used it as an example? so it could be 10 or something else

Doesn't matter, could be anything else.

Reply 7

I can do this

7

@Zacken any last minute tips for C2? Specifically really hard shapes/trig/coordinate geometry questions? :smile:

Reply 8

username2250433

13

Btw what formulas aren't on the sheet other than sector area/length and trapezium area that we need to know?

Reply 9

Zacken

22

Original post by I can do this

@Zacken any last minute tips for C2? Specifically really hard shapes/trig/coordinate geometry questions? :smile:

Yes: go to sleep! Seriously, staying up and trying to cram last minute is utterly useless. :smile:

Stay calm in the exam, remember your definitions, remember that volume = area of cross section * length and you're golden.

Reply 10

I can do this

7

Original post by Zacken

Yes: go to sleep! Seriously, staying up and trying to cram last minute is utterly useless. :smile:

Stay calm in the exam, remember your definitions, remember that volume = area of cross section * length and you're golden.

I'll take your word for it - I'm worried that I've not done a proper edexcel paper in a while because for the last few days I've been going cold turkey with solomon so I may not have covered everything on the spec :s Thank you! How did you do on all of your modules?

Reply 11

Zacken

22

Original post by I can do this

I'll take your word for it - I'm worried that I've not done a proper edexcel paper in a while because for the last few days I've been going cold turkey with solomon so I may not have covered everything on the spec :s Thank you! How did you do on all of your modules?

Don't worry, just relax. :tongue:

I've put up my grades here if you want to take a look, but I'm still sitting more modules, I've got S3 tomorrow as well. :tongue:

'Taking Logs'

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you