algebra
posted by Marissa .
1)Find a1 in a geometric series for which Sn=300,r=3,and n=4
a.15
b.15/2
c.15
d.1/15
answer=a
2)Find the sum of the infinite geometric series n=1 at the bottom of the sigma notation 20(1/4)n1 on the right side
a.25
b.80/3
c.16
d.does not exist
answer=c
3)Find the sum of the infinite geometric series :4+3+9/4+:...
a.16/7
b.16
c.12
d.does not exist
answer=c
4)Write Find the third iterate x3 o f(x)=x^24 for an initial value of x0=2
a.4
b.4
c.12
d.12
answer=c
5) Which is NOT a counterexample to the formula 1^2+3^2+5^2+...+(2n1)^2=n(2n+1)/3
a.n=3
b.n=2
c.n=1
d.n=4
answer=c

recheck 1,3
I don't understand 2 
do you know about sigma notation?