PreCalc
posted by Roy
Can someone show me how to do this please. I am stuck.
find a number x such that
e^2x – 12e^x =13

MathMate
Substitute y=e^x to get a quadratic equation:
y²12x+13=0
Solve for y.
Substitute the values of y=e^x into the original equation to make sure that all the roots are feasible/defined.
See also previous example:
http://www.jiskha.com/display.cgi?id=1291874924 
Reiny
let e^x = t
then
e^2x – 12e^x =13 becomes
t^2  12t  13 = 0
(t13)(t+1) = 0
t = 13 or t = 1
then e^x = 13 or e^x = 1
x = ln 13 or x = ln(1)
but in ln(a) a > 0
so x = ln 13 
MathMate
I slipped in the sign of the transformed equation. Instead of
y²12x+13=0
it should read
y²12x13=0
Go with Reiny's solution. 
Roy
Thank u both
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