The arithmetic series I have begins with 100, and increases in increments of 100. (so d=100, a1=100, a2=200, a3=300, etc)
The geometric series I have begins with 2 and increases in increments of 2. so r=2, a1=2, a2=4, a3=8, etc.)
I know the formulas an=d(n-1) + a1
and an=a1r^n-1
...but I...