Let $\alpha\in$ R be such that the function $$f(x) = \left\{ {\begin{matrix} {{{{{\cos }^{ - 1}}(1 - {{\{ x\} }^2}){{\sin }^{ - 1}}(1 - \{ x\} )} \over {\{ x\} - {{\{ x\} }^3}}},} & {x e 0} \\ {\alpha ,} & {x = 0} \\ \end{matrix} } \right.$$ is continuous at x = 0, where {x} = x $-$ [ x ] is the greatest integer less than or equal to x. Then :