Friedmann equations

[lucasgautheron]

• Add plots
• Express in terms of the density parameters rather than the densities themselves (less cluttered expressions)
• Fix eq. bug

\begin{equation}\left\{\begin{matrix}
                     a(t) = &A\cosh \left [ H_0 \sqrt{\Omega_{\Lambda}} (t-T) \right ] \\
                     T = &\pm \tau \tanh^{-1} \dfrac{1}{\sqrt{1+\dfrac{1-\Omega_{\Lambda}}{\Omega_{\Lambda}}}}} \\
                     A = &+\dfrac{3kc^4}{8 \pi G \rho_0 R^2} \\
                     \tau = & 1/H_0 \sqrt{\Omega_{\Lambda}} \\
                     \end{matrix}\right.\end{equation}

[lucasgautheron]

Done.