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# c2 problem..Help :) watch

1. Hi guys, I was wondering if you clever people could help me out on a question involving logarithms

I need to solve, 3^2x+3^x+1-10=0 (the ^ means to the power of)

I can do the last bit where i plug it into the calculator, however I cant get to that stage.

Thanks for the help in advance, a rep for the solver .
2. OK.
First you need to change it to:
3^2x + 3^x+1 = 10

Then you would use log to the base 3 on both sides to give:

2x + x+1 = log(to the base 3) 10

http://www.ltcconline.net/greenl/Cou...p/explogeq.htm

Scroll down to the first box that says Change of Base Formula.

You should be able to do it from there.
3. (Original post by foxyamy)
OK.
First you need to change it to:
3^2x + 3^x+1 = 10

Then you would use log to the base 3 on both sides to give:

2x + x+1 = log(to the base 3) 10

http://www.ltcconline.net/greenl/Cou...p/explogeq.htm

Scroll down to the first box that says Change of Base Formula.

You should be able to do it from there.
Thanks alot, I really appreciate the help. + rep (:
4. (Original post by ForTheWin)
Thanks alot, I really appreciate the help. + rep (:
That's OK - just hope that's the way they're expecting you to do it!! It's been a long time since I did A level maths
5. (Original post by foxyamy)
That's OK - just hope that's the way they're expecting you to do it!! It's been a long time since I did A level maths
Haa, dw it is. I don't think my teacher has ever changed her ways of teaching. And she's being doing it a ruddy long time! Anyway thanks, much appreciated.
6. (Original post by foxyamy)
OK.
First you need to change it to:
3^2x + 3^x+1 = 10

Then you would use log to the base 3 on both sides to give:

2x + x+1 = log(to the base 3) 10
You haven't applied the log laws correctly there.

It's a quadratic in 3^x - remember (3^x)^2 = 3^2x, let u = 3^x if you want. Solving the quadratic will give you values for 3^x, from these use logarithms to find the values of x
7. Don't really need to think about logs!! Just make sure they are all 3 (to the power of something) and then solve the powers like a normal equation!
8. Agreed, logging it is OTT and may show a lack of appreciation of the topic at C2

Most students forget to solve for the power after they factor the quad

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