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C2 Log queston.

How would you go about solving this?

Can you go through it in simple stages and stating any rules you are using, cheers question is q4 January 2009 edexcel.

Edit: Solved, forgive me I am a fool.

(edited 13 years ago)

Reply 1

Ben121

Assuming they are the same base you can say (4-x)/x^2 = 5

Reply 2

chaosdestro0

Original post by Ben121

Assuming they are the same base you can say (4-x)/x^2 = 5

Is it that easy? :O.
Pity the fool, I just wasted a good half hour trying to figure it out and did not know such a rule existed.

Reply 3

beelz

...

(edited 10 years ago)

Reply 4

LimeTree.

Original post by chaosdestro0

Is it that easy? :O.
Pity the fool, I just wasted a good half hour trying to figure it out and did not know such a rule existed.

Its not really a rule... more just thinking logically... or logarithically.. lol

Aslong as there the same base.. its the same as saying 2*(4-x)/x^2 = 2*5

...and you just divide both sides by 2 to get (4-x)/x^2 = 5.

Same kinda thing

Reply 5

j.alexanderh

Original post by chaosdestro0

Is it that easy? :O.
Pity the fool, I just wasted a good half hour trying to figure it out and did not know such a rule existed.

Sure. Just put the base of the log to the power of each side. Eg, if it's log to base e, then just use the exponential function on both sides and this will get rid of both logs.

Reply 6

HedonisticMe

Original post by beelz

lol its not really a rule, its just common sense

i wouldn't go as far to say that.

Reply 7

Evanesyne

Sorry to butt in, but could someone be so kind to talk me through the question please? I missed the lesson on this, so I'm not really sure how to go about it. Much appreciated :smile:

Reply 8

Ben121

You should know how to solve (4-x)/x^2 = 5 from core 1. Multiply both sides by x^2 and then you have a quadratic.

Reply 9

chaosdestro0

Original post by Ben121

You should know how to solve (4-x)/x^2 = 5 from core 1. Multiply both sides by x^2 and then you have a quadratic.

I know how to solve that :smile:

, I just fricken hate logs and they need to be nuked from orbit.
I can deal with them, but not apply logic towards as them. It might be due to the fact that we only just rush through them learning rules and not going into hard questions.

Reply 10

j.alexanderh

Original post by Evanesyne

Sorry to butt in, but could someone be so kind to talk me through the question please? I missed the lesson on this, so I'm not really sure how to go about it. Much appreciated :smile:

Do you know what logarithms are?

Reply 11

beelz

Original post by HedonisticMe

i wouldn't go as far to say that.

why not?

Reply 12

Evanesyne

Original post by j.alexanderh

Do you know what logarithms are?

Kind of.

But oh, I just realised my mistake. I've been trying to solve 4-x/x2 = log5, when it should have been just 5. I got x= 4/5 and -1. Is that right?

Reply 13

j.alexanderh

Original post by Evanesyne

Kind of.

But oh, I just realised my mistake. I've been trying to solve 4-x/x2 = log5, when it should have been just 5. I got x= 4/5 and -1. Is that right?