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

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: 7,979

### Re: Solving for x

Welcome to the forum.

That answer looks good to me.

Bob

Children are not defined by school ...........The Fonz
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

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
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Solving for x

Hi;

You can convert that expression on the right to be

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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

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
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### 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.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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

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: 7,979

### Re: Solving for x

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

Children are not defined by school ...........The Fonz
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

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: 7,979

### Re: Solving for x

OK.  That'll do.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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