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How do you solve this? 

 

ex - 6e-x = 1

 Oct 6, 2015

Best Answer 

 #2
avatar+118667 
+15

ex - 6e-x = 1

 

\(e^x-6e^{-x}=1\\\\ e^x-\frac{6}{e^{x}}=1\\\\ e^x(e^x-\frac{6}{e^{x}})=1*e^x\\\\ (e^x)^2-6=e^x\\\\ (e^x)^2-e^x-6=0\\\\ sub\;y=e^x\\\\ y^2-y-6=0\\\\ (y-3)(y+2)=0 y=3\;\;or\;\;y=-2\\\\ e^x=3\;\;or\;\;e^x=-2\\\\ lne^x=ln3\;\;or\;\;no\; solution\\\\ x=ln3 \)

 Oct 6, 2015
 #1
avatar+129845 
+15

ex - 6e-x = 1      multiply through by ex

 

e2x - 6 = ex      subtract  ex  from both sides and rearrange the left side

 

e2x - ex - 6 =  0     factor this

 

(ex - 3) (ex + 2) =     setting each factor to 0, we have

 

ex - 3 = 0                                   and                             ex + 2 = 0

 

The second equation has no solution.....for the first, we have

 

ex - 3 = 0

 

Add 3 to both sides

 

ex  = 3       take the ln of both sides

 

ln e= ln 3      and we can write

 

x ln e =   ln 3     and ln e = 1, so we can ignore this.......and we have

 

x = ln 3 = about 1.0986

 

 

cool cool cool

 Oct 6, 2015
 #2
avatar+118667 
+15
Best Answer

ex - 6e-x = 1

 

\(e^x-6e^{-x}=1\\\\ e^x-\frac{6}{e^{x}}=1\\\\ e^x(e^x-\frac{6}{e^{x}})=1*e^x\\\\ (e^x)^2-6=e^x\\\\ (e^x)^2-e^x-6=0\\\\ sub\;y=e^x\\\\ y^2-y-6=0\\\\ (y-3)(y+2)=0 y=3\;\;or\;\;y=-2\\\\ e^x=3\;\;or\;\;e^x=-2\\\\ lne^x=ln3\;\;or\;\;no\; solution\\\\ x=ln3 \)

Melody Oct 6, 2015
 #3
avatar+129845 
+5

HAHAHAHAHA!!!!!!!!.......beat you, Melody   !!!!!!    LOL!!!!!!!

 

 

 

 

cool cool cool

 Oct 6, 2015

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