$k$, $c_1$ and $c_2$ are unkowns, while others are given. How can I solve the equations?
$$ \begin{cases} k\left( {c_1 e^{\pi k} + \frac{c_2}{e^{\pi k}}} \right)^{(1 + 2\theta)/\theta} = - \theta^2\tau \\ k(c_1 + c_2)^{(1 + 2\theta)/\theta} = \theta^2\tau \frac{e^ -\theta\eta - 1}{e^{-\theta\eta} + 1}\\ k\left( \frac{c_1}{e^{\pi k}} + c_2 e^{\pi k} \right)^{(1 + 2\theta)/\theta} = \theta^2\tau \end{cases} $$