Logarithms

Hi, I'm not sure how to answer this question.

If 2log_an - log_a (5n - 25) = log_a4 find the value of n.

The answer and how to do it would be appreciated. Thanks! :smile:

Reply 1

wdkmwd

3

As a Computer scientist I'll do my job and tag a person who should answer this easily

@Zacken

Reply 2

oinkk

3

Line 2: Raise the 2 up as a power of n.
Line 3: Use the subtraction law and divide both logs (since they are to the same base of a)
Line 4: Technically, you can raise both sides as a power of 'a', thus cancelling the a and the loga terms to leave a quadratic that you can solve. If that doesn't make sense, then you can just equate whatever is inside the brackets of the logs since they are to the same base of a.

Now it is just a quadratic to solve.

Any questions, give me a shout :-)

(edited 8 years ago)

Reply 3

Zacken

22

Original post by oinkk

Any questions, give me a shout :-)

Full solutions are against forum guidelines.

Reply 4

username2302349

OP

1

Original post by oinkk

Line 2: Raise the 2 up as a power of n.
Line 3: Use the subtraction law and divide both logs (since they are to the same base of a)
Line 4: Technically, you can raise both sides as a power of 'a', thus cancelling the a and the loga terms to leave a quadratic that you can solve. If that doesn't make sense, then you can just equate whatever is inside the brackets of the logs since they are to the same base of a.

Now it is just a quadratic to solve.

Any questions, give me a shout :-)

Thank you so much! :smile:

Reply 5

oinkk

3

Original post by cassie05

Thank you so much! :smile:

My pleasure! :smile:

Reply 6

wdkmwd

3

Original post by Zacken

Full solutions are against forum guidelines.

Doesn't look like he cares mate.

Reply 7

username1560589

20

Figure out a way to get rid of the logs. Solve the resulting equation.

Reply 8

Student403

19

Original post by wdkmwd

Doesn't look like he cares mate.

Which is a shame because full solutions don't help the OP as much as people think they do

Reply 9

wdkmwd

3

Original post by Student403

Which is a shame because full solutions don't help the OP as much as people think they do

OP Got his answer, and i got my clever clogs badge.

Everyone's happy

Reply 10

Student403

19

Original post by wdkmwd

OP Got his answer, and i got my clever clogs badge.

Everyone's happy

Reply 11

thefatone

6

Original post by wdkmwd

OP Got his answer, and i got my clever clogs badge.

Everyone's happy

derp not everyone...

Original post by Student403

Reply 12

wdkmwd

3

Original post by Student403

Reply 13

wdkmwd

3

Original post by thefatone

derp not everyone...

:colondollar:

k.

Reply 14

ombtom

17

Original post by Student403

Which is a shame because full solutions don't help the OP as much as people think they do

Maybe I'm just being weird again, but a full solution usually helps me a lot, because then I can work through it and see where I get stuck, and ask for help with that bit. And I can check if I've just made a simple mistake. I suppose everyone's different, and we need the "no full solutions" rule to benefit the majority. :smile:

Reply 15

Zacken

22

Original post by ombtom

Maybe I'm just being weird again, but a full solution usually helps me a lot, because then I can work through it and see where I get stuck, and ask for help with that bit. And I can check if I've just made a simple mistake. I suppose everyone's different, and we need the "no full solutions" rule to benefit the majority. :smile:

You'd benefit more from being prodded along bit by bit, trust me - it really builds your mathematical ability. If you've made a simple mistake, then the best thing is for you to have posted your working and somebody else to just point that out for you. :-)

Reply 16

ombtom

17

Original post by Zacken

If you've made a simple mistake, then the best thing is for you to have posted your working and somebody else to just point that out for you. :-)

True.

Reply 17

Student403

19

Original post by ombtom

Maybe I'm just being weird again, but a full solution usually helps me a lot, because then I can work through it and see where I get stuck, and ask for help with that bit. And I can check if I've just made a simple mistake. I suppose everyone's different, and we need the "no full solutions" rule to benefit the majority. :smile:

Imagine giving the OP "full solutions" as how people use the "Solution bank". You go to it when you're stuck and work through it and then you get it. The problem is Solution Banks aren't for everyone. You have to be very critical to be able to fully utilise it, because it will show you niche aspects of the question/solution that you might overlook. People often read a full solution and go "oh I'll get that in the exam" but this is definitely not the case all the time. This can be helpful but it's nowhere near as helpful as getting there yourself - writing the solution yourself.

It's sort of like the difference between theory and practical. In the former, you'll read it and it will definitely teach you something, but it's so easy to read over something that might have been a key aspect you'd have found out through your own experience, had you done the practical.

tl;dr full solutions can be helpful, but definitely not as much as getting there yourself :smile:

edit: to add, I can see the solution bank being useful for people like you because you're of the ability that you'll be much more likely to pick up the nitty gritty parts, but people on here are all different and rather than "assess" each one to determine if he/she is worthy of the straight solution, it helps everyone (some more than others) to be guided through the question instead

(edited 8 years ago)

Reply 18

ombtom

17

Original post by Student403

tl;dr full solutions can be helpful, but definitely not as much as getting there yourself :smile:

edit: to add, I can see the solution bank being useful for people like you because you're of the ability that you'll be much more likely to pick up the nitty gritty parts, but people on here are all different and rather than "assess" each one to determine if he/she is worthy of the straight solution, it helps everyone (some more than others) to be guided through the question instead