Please help!
Find S_n for each series described. You will need to determine if the series is arithmetic or geometric.

1. 160 + 80 + 40 + ....., n=6

2. d= -2/3, n= 16, a_n= 44

Question

Please help!
Find S_n for each series described. You will need to determine if the series is arithmetic or geometric.

1. 160 + 80 + 40 + ....., n=6

2. d= -2/3, n= 16, a_n= 44

anonymous · Answer

looks like they are dividing by two each time for the first one

clamin · Answer

How do i solve it? @satellite73

anonymous · Answer

This should be a geometric progression since the difference in two terms is not constant
You would need to find the (r) ratio in which the terms decrease, this can be done by dividing the second term by the first term

r = 1/2

the formula for the sum of geometric progression 
$$S_{n} = \frac{a(1-r^{n})}{1-r}$$

clamin · Answer

Which is it for @thushananth01? Question 1 or 2?

anonymous · Answer

1

clamin · Answer

How do i solve the 2nd? @thushananth01

anonymous · Answer

Use the formula for arithmetic progression
$$S_n = \frac{n}{2}(2a + (n-1)d)$$

clamin · Answer

What do i substitute with 2a?? @thushananth01

anonymous · Answer

That should be a_n

clamin · Answer

Ok