Question

is there two different ways of going about solving these two problems?

Answer 1

my first problem is
Find S20 of the arithmetic series 14 + 16 + 18 + 20 +...

my second one is
Find S12 for the series 2 + 5 + 8 +...

the only word that is different is "arithmetic." do i use the same method for solving both problems?

Answer 2

absolutely same method.

in 2nd problem, its not given that its an arithmetic series, but we can figure it out.
find the common difference between the terms, if it comes out to be same , its arithmetic sequence
if 8-5=5-2 ......

Answer 3

and you know the method or formula to find the sum ?

Answer 4

how do i write the equation for something like
Find S8 for the series -2 + -10 + -50 + -250 +...

like the change in numbers is different. does this make sense.

Answer 5

i know the equation is tn = t1 + (n-1)d

Answer 6

but i don't know how i find t1 for something like this

Answer 7

yes, for -2 + -10 + -50 + -250

check the common ratio!
-10/-2 =... ?
-50/-10=... ?
-250/-50 =...?

you know sequences can be Arithmetic or Geometric, right ?

Answer 8

when there is a common ratio, the sequence is geometric :)

Answer 9

tn = t1 + (n-1)d
t1 is the FIRST term of the sequence!

Answer 10

d is the difference. my bad

Answer 11

what doubt you still have ?

Answer 12

what do you mean?

Answer 13

i mean what questions you have ?
could you do the first one you asked ?
finding sum of those 2 sequences ?

Answer 14

is this the Q, you could still not answer ?
"how do i write the equation for something like
Find S8 for the series -2 + -10 + -50 + -250 +..."