$\sum_{n=0}^{\infty} 2 \cdot (-3)^n x^n$ for $|x| < \frac{1}{3}$

$\sum_{n=0}^{\infty} 2 \cdot 3^n x^n$ for $|x| < \frac{1}{3}$

$\sum_{n=0}^{\infty} (-1)^n 3^n x^n$ for $|x| < 1$

$\sum_{n=0}^{\infty} 2 \cdot (-3)^n x^n$ for $|x| < 1$