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How do I solve (e^-0.2x)-(e^-0.75x)=0.25?

 May 12, 2014

Best Answer 

 #4
avatar+33657 
+5

It is also possible that the equation in question is meant to be:

e0.2xe0.75x=0.25 

In this case there are two solutions as can be seen from the graph below:

efn

These solutions can be obtained numerically.  A simple iterative approach is to write the equation in the following form:

xn+1=10.2ln(0.25+e0.75xn) 

Then let x0 = 1, say, and use the formula above to iterate several times.  The result is:

x ≈ 6.812073

By rewriting the iteration formula as:

xn+1=10.75ln(e0.2xn0.25)

we can iterate to the other solution:

x ≈ 0.6023554654

 May 12, 2014
 #1
avatar+118703 
+5

How about with the site calculator?

e(0.2)×0.25e(0.75)×0.25=0.0865910500842418

 

I am not sure if this is actually what you meant - you must be careful to check the brackets are in the right place.

(It is what you asked i believe)

 May 12, 2014
 #2
avatar+130477 
+5

Maybe you meant this:

e^(-.2) x  - e^(-.75) x  = .25 ??

I'm going to assume so......So we have

0.8187307530779818 x - 0.4723665527410147 x = .25

0.3463642003369671 x = .25        So x = .25 / 0.3463642003369671 = 0.7217836016446927047

 

 May 12, 2014
 #3
avatar+118703 
0

 

Chris thinks you meant

(e0.2×x)(e0.75×x)=0.25

Yes, this probably is what you meant.  Your title is missing a bracket so there is plenty of room for confusion!

I read in an extra x (without even realising) and Chris read in an extra bracket.  I now see your main text does have the bracket!

 May 12, 2014
 #4
avatar+33657 
+5
Best Answer

It is also possible that the equation in question is meant to be:

e0.2xe0.75x=0.25 

In this case there are two solutions as can be seen from the graph below:

efn

These solutions can be obtained numerically.  A simple iterative approach is to write the equation in the following form:

xn+1=10.2ln(0.25+e0.75xn) 

Then let x0 = 1, say, and use the formula above to iterate several times.  The result is:

x ≈ 6.812073

By rewriting the iteration formula as:

xn+1=10.75ln(e0.2xn0.25)

we can iterate to the other solution:

x ≈ 0.6023554654

Alan May 12, 2014

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