Arithmetic sequences: sum of 1st n terms is 2 times sum of 1st 5 terms....

[mxo11]

hello
the question :
Arithmetic sequences : term 36 =0 . the
sum of the first n terms is 2 times the sum of the first 5 terms.
Find n ?

 

[tkhunny]

You should have a formula for the sum of a number of terms of an arithmetic series. Please state it.

How can you use it to solve this problem?

You an also create the formula yourself.

"a" is the first term.
"d" is the common difference.

Here's n terms, added up.
a + (a+d) + (a+2d) + ... + (a +(n-1)d)
Add those up!