Arithmetic and Geometric Series!

To find the sum of the ___ terms of an arithmetic series

Sn=n(t1+tn)/2

To find the sum of the ___ terms of a geometric series

Sn=t1(1-r^n)/1-r

Series- a list of numbers that are added together.

1+3+5+9+...

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Ex.1:

Find the sum of the series 1-3+5-7+9-11+...+1001.

S501=501(1+1001)/2

S501=251001

1001=1+(n-1)2

1001=1+2n-2

1001=-1+2n

1002=2n

n=501

Ex.2:

For the arithmetic series, find the specified sum.

S50=: 5+10+15+...

S50=50(5+250)/2

S50=6375

tn=t1(n-1)d

tn=5+(50-1)5

tn=5+250-5

tn=250