1
Q
Nth term for arithmetic sequence
A
A+(n-1)d
2
Q
Arithmetic series - sum
A
Sn= 1/2 n( 2a +( n-1)d)
3
Q
How to prove the arithmetic Series
A
Write out series one way, then reverse it. Add together to get 2sn
simplify In for
4
Q
Nth term for geometric sequence
A
ar^n-1
5
Q
Geometric series - sum of n
A
a(1-r^n)/1-r
OR
a(r^n -1)/r-1
6
Q
Proving the geometric sequence
A
Write out Sn for geometric
Multiply by r
Do Sn - rSn
Get Sn(r-1)=a-ar^n
Simplifies to Sn = a (1-r^n)/1-r
7
Q
What does convergent mean
A
In geometric sequences:
Terms decrease as n increases
8
Q
What is the geometric sum to infinity
A
Sn= a/1 -r
For modulus r <1
( /r/ <1)
