Direct proof As with any infinite series, the infinite sum 1 2 + 1 4 + 1 8 + 1 16 + ⋯ {\displaystyle {\frac {1}{2}}+{\frac {1}{4}}+{\frac {1}{8}}+{\frac {1}{16}}+\cdots } is defined to mean the limit of the sum of the first n terms