What is the sum of the first 18 terms of the arithmetic series
11 + 15 + 19 + 23 + ⋯?

Question

What is the sum of the first 18 terms of the arithmetic series
11 + 15 + 19 + 23 + ⋯?

zzr0ck3r · Answer

all I really used is that $\sum_{i=1}^ni=\frac{n(n+1)}{2}$

anonymous · Answer

is it 810
?

zzr0ck3r · Answer

$\sum_{n=1}^{18}7+4n=\sum_{n=1}^{18}7+4\sum_{n=1}^{18}n=18*7+4(\frac{18*19}{2})=810$

zzr0ck3r · Answer

yes:)

anonymous · Answer

thanks

zzr0ck3r · Answer

how did you do it, so I know how to explain it to others without the notation and method I used.

anonymous · Answer

i did it the hard way just adding 4 to every number and just add until you reach the 18th term

zzr0ck3r · Answer

oh well notice with my way you can now do the 1200000th term

zzr0ck3r · Answer

just change where you see an 18 to 1200000

anonymous · Answer

yeah and thanks

zzr0ck3r · Answer

ok good luck, if you ask another someone else might have an easier way. I know there is, but I never studied arithmetic sequences....

hartnn · Answer

there is a simple formula for sum of terms in an arithmetic sequences.  
you just need 1st term, common difference and number of terms