Which of the following infinite geometric series has a finite sum?
1+2+4+8+16+...1 + 2 + 4 + 8 + 16 + ...1+2+4+8+16+...
3+6+12+24+...3 + 6 + 12 + 24 + ...3+6+12+24+...
12+14+18+116+...\frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \frac{1}{16} + ...21+41+81+161+...
2−4+8−16+32−...2 - 4 + 8 - 16 + 32 - ...2−4+8−16+32−...