501 Вычислите: а) (2/5)^2; б) (3/4 - 2/3)^2; B) (1/2)^3 - (1/4).

<table> <tr><td>a) $$\left(\frac{2}{5}\right)^2 = \frac{2^2}{5^2} = \frac{4}{25} = 0.16$$</td></tr> <tr><td>б) $$\left(\frac{3}{4} - \frac{2}{3}\right)^2 = \left(\frac{9}{12} - \frac{8}{12}\right)^2 = \left(\frac{1}{12}\right)^2 = \frac{1}{144} \approx 0.00694$$</td></tr> <tr><td>в) $$\left(\frac{1}{2}\right)^3 - \frac{1}{4} = \frac{1}{8} - \frac{1}{4} = \frac{1}{8} - \frac{2}{8} = -\frac{1}{8} = -0.125$$</td></tr> </table>