2014-04-23 MathJax 練習 MathJax 数学 $$1 + 1 +\frac{1}{2}+\frac{1}{2^2}+\cdots+ \frac{1}{2^n-1} = 1 + \frac{1 - (\frac{1}{2})^n}{1 - \frac{1}{2}}$$