hitunglah n jika 1 + 2 + 4 + ...+2pangkat n-1 =127 (jumlah deret geometri =127)

[tex]$\begin{align}S_n&=\frac{a\left(r^n-1)}{r-1}\\127&=\frac{1\left(2^n-1\right)}{2-1}\\127&=2^n-1\\2^n&=128\\2^n&=2^7\\n&=\boxed7\end[/tex]