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 Post subject: exponential equationPosted: Mon, 28 Nov 2011 18:46:15 UTC
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e^4x+4e^2x-21=0
I think I'm supposed to substitute u=e^2x so then i got u=either -7 or 3 but where do I go from there?

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 Post subject: Re: exponential equationPosted: Mon, 28 Nov 2011 19:20:33 UTC
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The -7 does not correspond to a real root. You can take logs to solve for the other root.

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 Post subject: Re: exponential equationPosted: Mon, 28 Nov 2011 19:42:12 UTC
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so solve for 3 and not -7?

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 Post subject: Re: exponential equationPosted: Mon, 28 Nov 2011 23:01:38 UTC
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Peaches1113 wrote:
so solve for 3 and not -7?

It depends on what grade you are in. If you have been exposed to complex numbers, you need both. Otherwise solution for 3 will do.

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 Post subject: Re: exponential equationPosted: Mon, 28 Nov 2011 23:46:16 UTC
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Joined: Wed, 30 Mar 2005 04:25:14 UTC
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mathematic wrote:
Peaches1113 wrote:
so solve for 3 and not -7?

It depends on what grade you are in. If you have been exposed to complex numbers, you need both. Otherwise solution for 3 will do.

This is the algebra forum, not the analysis forum. CONTEXT.

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 Post subject: Re: exponential equationPosted: Tue, 29 Nov 2011 23:11:51 UTC
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Shadow wrote:
mathematic wrote:
Peaches1113 wrote:
so solve for 3 and not -7?

It depends on what grade you are in. If you have been exposed to complex numbers, you need both. Otherwise solution for 3 will do.

This is the algebra forum, not the analysis forum. CONTEXT.

That is a strange assertion. Complex numbers are usually introduced into algebra courses, once you are trying to solve x^2 + 1 = 0.

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 Post subject: Re: exponential equationPosted: Tue, 29 Nov 2011 23:14:38 UTC
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Joined: Wed, 30 Mar 2005 04:25:14 UTC
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mathematic wrote:
Shadow wrote:
mathematic wrote:
Peaches1113 wrote:
so solve for 3 and not -7?

It depends on what grade you are in. If you have been exposed to complex numbers, you need both. Otherwise solution for 3 will do.

This is the algebra forum, not the analysis forum. CONTEXT.

That is a strange assertion. Complex numbers are usually introduced into algebra courses, once you are trying to solve x^2 + 1 = 0.

But solving for values of the exponential which give negative values comes from Euler's formula, introduced in a precalculus or calculus, not in algebra.

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 Post subject: Re: exponential equationPosted: Thu, 1 Dec 2011 00:33:17 UTC
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I have no expertize on math curricula. In my student days, there was no such thing as "precalculus". What I took (senior year in high school) was called "advanced algebra". I suspect it covered the same material, including Euler's formula.

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 Post subject: Re: exponential equationPosted: Thu, 1 Dec 2011 00:39:51 UTC
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mathematic wrote:
I have no expertize on math curricula. In my student days, there was no such thing as "precalculus". What I took (senior year in high school) was called "advanced algebra". I suspect it covered the same material, including Euler's formula.

I suspect that is where our disconnect is then, a standard senior level class does cover such things, but in the form of "precalculus [and trig]", rather than the second algebra class which -- though they do briefly introduce complex numbers -- does not deal with them very thoroughly, and certainly not at the level of Euler's formula.

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