\(f(x)=\sqrt{x^2-1}\), \(g(x)=\sqrt{1-x}\)
Solución
\[\begin{eqnarray*} % Espacio entre filas aumentado \\[0.2cm] (f\circ g)(x) & = & f(g(x)) \\[0.2cm] & = & f(\sqrt{1-x}) \\[0.2cm] & = & \sqrt{(\sqrt{1-x})^2-1} \\[0.2cm] & = & \sqrt{1-x-1} \\[0.2cm] & = & \sqrt{-x} \\[0.2cm] \end{eqnarray*}\]