Each of these sequence or series formulas involves four quantities. For each formula, describe the four quantities. Then explain how you can find the forth quantity if you know the values of the other three.
a)An=a1+(n-1)d
b)Sn=n/2(a1+an)
c)An=a1r^(n-1)
d)Sn=(A1(1-r^n)/(1-r)