Hi,
please find attached the problem and the short and sweet Answer.
I can't understand the last step of the answer.
$\displaystyle
-2e^k + 4e^{-k} = -2
$
Moving everything to the left
$\displaystyle
-2e^k + 2 + 4e^{-k} = 0
$
Factorising $\displaystyle -2e^{-k} $
$\displaystyle
-2e^{-k}(e^{2k} - e^k -2) = 0
$
Divide both sides by $\displaystyle -2e^{-k}$
$\displaystyle
e^{2k} - e^k -2 = 0
$