V
vanquan238


Rút gon:
$$A=tanx+\frac{1}{2}tan\frac{x}{2}+...+\frac{1}{{2}^{n}}tan\frac{x}{{2}^{n}}$$
$$A=tanx+\frac{1}{2}tan\frac{x}{2}+...+\frac{1}{{2}^{n}}tan\frac{x}{{2}^{n}}$$
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