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# Indices watch

1. solving questions where the indice is unknown
simple example being 5^x=125
is trial and error the only method?
coz i have more complicated ones to solve where
something^x= surd
2. 5^3 = 125

Not sure if that's what you after.
3. no
i want a method
that was just a simple example
if you got say 5^x= 10 root6 (again just an example)
4. 5^x = 125
log5^x = log125
x log5 = log 125
x = log125/log5
= 3

logarithms

Btw this is A2 maths so if you're only at GCSE you don't need to know that.

In your more complicated example follow the same method to get x = 1.98731...
5. mik1a
AS student
haven't done log
and we've been given the complicated example types?????
6. Well that's what I've picked up, I haven't done logs either but when you stay on these forums you learn some useful things

I think that's the only way you can do it with complicated examples, unless your examples have x as a power on both sides, in which case you can change the actual number below the x to make them equal on either side and equate the xs:

That wasn't very clear so here's an example:

2^x = 8^(x-3)

we know that 8=2^3

so

2^x = (2^3)^(x-3)
2^x = 2^(3*(x-3))
2^x = 2^(3x-9)

then obviously

x = 3x-9
2x = 9
x = 4.5

You need to remember indices and surds rules and mess around with the equation to try to give you x=? If you weren't taught logs and are set those questions then there's probably some subtle way to do it.
7. Logs are in AS
8. P1 for OCR and AQA, P2 Edexcel I think.
9. (Original post by mik1a)
P1 for OCR and AQA, P2 Edexcel I think.
yup.

if you ahvent done logs yet then trial and error is the way
10. What you need to do is get the bases's the same and then it becomes easy...

So for example

5^x = 125

Make the bases equal...

5^x = 5^3

Now you can 'forget' about the fives so to speak, and look at just the powers. Therefore you get x = 3.

This is the method explained by mik1a pretty much..
11. (Original post by imasillynarb)
What you need to do is get the bases's the same and then it becomes easy...

So for example

5^x = 125

Make the bases equal...

5^x = 5^3

Now you can 'forget' about the fives so to speak, and look at just the powers. Therefore you get x = 3.

This is the method explained by mik1a pretty much..
Thats the OCR P1 way, in logs dont come until OCR P2
12. (Original post by cobra01977)
Thats the OCR P1 way, in logs dont come until OCR P2
We learn that method in P1 and then learn logs in P2..for edexcel
13. You can also use clever tricks to change power and number:

2√9 = |√4√9| = |√36| = 6
12√8 = 3*0.25*√8 = 3√0.5√8 = 3√4
10√9 = |√100√9| = |√900| = 30

Cool huh
14. (Original post by mik1a)
12√8 = 3*0.25*√8 = 3√0.5√8 = 3√4
Uh???

12√8 = 3*4*√8 = 3√128...if thats what you want.

12√8 = 12(√4√2) = 24√2
15. (Original post by 2776)
Uh???

12√8 = 3*4*√8 = 3√128...if thats what you want.

12√8 = 12(√4√2) = 24√2
Yeah that's the one... 3*0.25 = 12?...

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