Tính nhanh biểu thức dưới đây: 1/2 + 1/4 + 1/8 + 1/16 + 1/32 + 1/64 + 1/128

\[\frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \frac{1}{{16}} + \frac{1}{{32}} + \frac{1}{{64}} + \frac{1}{{128}}\]

\[ = 1 - \frac{1}{2} + \frac{1}{2} - \frac{1}{4} + \frac{1}{4} - \frac{1}{8} + \frac{1}{8} - \frac{1}{{16}} + \frac{1}{{16}} - \frac{1}{{32}} + \frac{1}{{32}} - \frac{1}{{64}} + \frac{1}{{64}} - \frac{1}{{128}}\]

\[ = 1 - \frac{1}{{128}} = \frac{{127}}{{128}}.\]