Let ${\alpha }_{\mathrm{r}}={\mathrm{e}}^{\mathrm{i}\frac{2\pi }{n}}(1\le \mathrm{r}\le \mathrm{n})$ be the complex number associated with the point A_r on Argand  plane, and point B is (2, 0) then the value of  ${\mathrm{BA}}_1\cdot {\mathrm{BA}}_2\cdot {\mathrm{BA}}_3\dots \dots {\mathrm{BA}}_n$is equal to