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

PreCalc 
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 
PreCalc 
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 
oops 
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. 
PreCalc 
Roy
Thank u both
Respond to this Question
Similar Questions

PreCalc
I'm stuck on a precalc problem. I need to find y as a function of x, where the constant c is a positive number for In(y1)+In(y+1)= x+c express your question as ln[(y1)(y+1)] = x+c change that to exponential form e^(x+c) = (y1)(y+1) … 
Algebra/PreCalc
Find the values for a and b such that f(x) is continuous on the interval 0 < or = to x < or = to 13. { 2x^2, 0 < or = to x < or = to 3 f(x) = { ax + 3, 3 < or = to x < or = to 7 { b, 7 < or = to x < or = to … 
PreCalc
I am stuck solving this problem, any help please..Many thanks find all numbers x that satisfy the given equation ln(2x)  =2 ln(3x) 
PreCalc
I'm so stuckthis stuff is so far above me right nowPlease help (3x^35^2+6x9)/(x+5) or can someone direct me to a site that can solve this and show the stepsI don't even know where to start Thank you 
PreCalc
I'm so stuckthis stuff is so far above me right nowPlease help where do I even start? 
PreCalc
Can you show me how to find the rectangular equation of r=2costheta + 3 sin theta All I need is an example to work off I was absent today from PreCalc and I have homework to do and no explanation with themPlease help with this one … 
PreCalc
Could someone show me how to solve these two problemsI have 10 of each kind to do this weekend and I'm really lost 1. Find product of 8(cos pi/2 + i sin pi/2) * 1/2(cos pi/6 + i sin pi/6) 2. Same problem but find quotient instead … 
algebra
find the LCM of 15ef and 12e^4 (12e to the power of 4) Please show the steps. I do not understand how to do this. 
PreCalc
Please help stuck on this one question Find (fog)(2) and (f+g)(2) when f(x)= 1/x and g(x)=4x+9 
pre calc
Can someone please help me f(x)=1/3 square root 12x and g(x)= (x2)/x. Find and simplify (g of g)(3)/(g of f)(24). The answer I got it 24/7 and i Am unsure If it is correct. Please show all work Thank you