(a) Start with \(y = \frac{x^2 - 4}{x^2 + 4}\). Clear the denominator: \((x^2 + 4)y = x^2 - 4\). Expand and rearrange: \(x^2 y + 4y = x^2 - 4\). Isolate \(x^2\): \(x^2 (1 - y) = 4y + 4\). Solve for \(x^2\): \(x^2 = \frac{4y + 4}{1 - y}\). Solve for \(x\): \(x = \frac{\sqrt{4y + 4}}{\sqrt{1 - y}}\). Thus, \(f^{-1}(x) = \frac{4x + 4}{1 - x}\).

(b) Start with \(1 - \frac{8}{x^2 + 4}\). Use a common denominator: \(\frac{x^2 + 4 - 8}{x^2 + 4} = \frac{x^2 - 4}{x^2 + 4}\). Therefore, the range of \(f\) is \(0 < f(x) < 1\).

(c) The composite function \(ff\) cannot be formed because the range of \(f\) does not include the whole of the domain of \(f\) (or any of it).