Find the sum of the first 12 terms of the sequence. Show all work for full credit.

1, -4, -9, -14, . . .

Question

Find the sum of the first 12 terms of the sequence. Show all work for full credit.

1, -4, -9, -14, . . .

phi · Answer

You could list out each term, then after have 12 of them, add them up.  
But there are short cut formulas.  

Do you know the formula to find the 12th term of a sequence?

anonymous · Answer

no

phi · Answer

Are you supposed to have learned it?

anonymous · Answer

yes

phi · Answer

In that case,  here it is  (Put this in your notes.. personally I just look it up if I need it.. but if you have to take a test, I suppose you have to memorize it )

$$ a_n=  a_1 + (n-1) d $$

that says to find the nth term,  you need to know the first term  (that is a1), and you need the difference between terms (that is d)

to find d,   use  

d=  a2 - a1

phi · Answer

to find d you need a2 and a1
1, -4, -9, -14, 

a1 is the 1st number. It is 1
a2 is the 2nd number It is -4

d =  a2-a1
can you find d?