If the functions are defined as $f(x) = \sqrt x $ and $g(x) = \sqrt {1 - x} $, then what is the common domain of the following functions :f + g, f $-$ g, f/g, g/f, g $-$ f where $(f \pm g)(x) = f(x) \pm g(x),(f/g)x = {{f(x)} \over {g(x)}}$