If the number of terms in the expansion of n 2 2 4 1 x x æ ö – + ç ÷ è ø , x ¹ 0, is 28, then the sum of the coefficients of all the terms in this expansion, is :

If the number of terms in the expansion of $\left(1-\frac{2}{x}+\frac{4}{x^{2}}\right)^{\mathrm{n}}$, $x \neq 0$, is 28 , then the sum of the coefficients of all the terms in this expansion, is: