# [SOLVED] Stuck on the next step

• Feb 3rd 2010, 11:42 AM
vinson24
[SOLVED] Stuck on the next step
Solve $e^{-2x}-3e^{-x}=-2$ for x without using a calculator

Now the first step i did was make it into a quadratic equation
$e^{-2x}-3e^{-x}+2=0$
Then i let $u=e^{-x}$
which gives me $u^{x}-3u+2=0$
now im kinda stuck on the next step becuase of the $u^{x}$ in the equation, not sure if i started of wrong or if im missing something thats right in front of me
• Feb 3rd 2010, 11:50 AM
Plato
Multiply by $e^{2x}$ to get $2e^{2x}-3e^{x}+1=0$.
• Feb 3rd 2010, 12:01 PM
vinson24
at which point in the problem are you multiplying $e^{2x}$ because i dont see where the $2e^{2x}$is coming from and the 1 at the end either
• Feb 3rd 2010, 12:03 PM
wonderboy1953
Correction
It's not $u^x$, it's $u^2$ in your last equation.
• Feb 3rd 2010, 01:04 PM
Plato
Quote:

Originally Posted by Plato
Multiply by $e^{2x}$ to get $2e^{2x}-3e^{x}+1=0$.

You must know basic algebra in order to do calculus.
$e^{-2x}(e^{2x})-3e^{-x}(e^{2x})=-2(e^{2x})$.