Ответ: a) a = 0, a = $$\frac{1}{4}$$, a = $$\frac{1}{5}$$, a = $$\frac{3}{8}$$; б) b = 5,5, b = 6, b = 7, b = 7,99; в) c = 9,6, c = 9,75, c = 10, c = 10,2.