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#1 2012-12-03 00:55:15

gbrad88
Member
Registered: 2012-12-03
Posts: 16

Solving for x

I am solving for X below:

4^(3x+5) = 1/256


The answer I get is -3 please correct me if I am wrong and why if you can please. Much appreciated.

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#2 2012-12-03 00:58:52

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,465

Re: Solving for x

hi gbrad88

Welcome to the forum.

That answer looks good to me.

smile

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#3 2012-12-03 02:15:20

gbrad88
Member
Registered: 2012-12-03
Posts: 16

Re: Solving for x

Sometimes I get x = -1/3 so Im not sure whats the right way to do it. :-(

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#4 2012-12-03 02:18:34

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 88,517

Re: Solving for x

Hi;

You can convert that expression on the right to be

does that help you?


In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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#5 2012-12-03 02:23:03

gbrad88
Member
Registered: 2012-12-03
Posts: 16

Re: Solving for x

I'm not sure. I think I don't understand.

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#6 2012-12-03 02:26:14

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 88,517

Re: Solving for x

You now have

Here is a trick to these types whenever the bases are the same


you can ignore them and just solve the equation that you get from the exponents.


In mathematics, you don't understand things. You just get used to them.

I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.

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#7 2012-12-03 05:12:01

gbrad88
Member
Registered: 2012-12-03
Posts: 16

Re: Solving for x

That trick makes a lot of sense, but, what about when one number cannot be the same? Like the 6 below:

3^x+7=6

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#8 2012-12-03 05:45:38

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,465

Re: Solving for x

hi gbrad88,

I'd do it like this:

Unfortunately, that's where this question unravels because you'd need to go into complex number theory to sort out log(-1).

This sort of thing happens if you make up a question at random.  (And you thought it was easy for a teacher to throw some questions together)

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#9 2012-12-03 06:05:17

gbrad88
Member
Registered: 2012-12-03
Posts: 16

Re: Solving for x

Maybe if I re-write it.

3^(x+7)=6

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#10 2012-12-03 06:12:15

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,465

Re: Solving for x

OK.  That'll do.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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