Find the sum of the first 12 terms of the sequence.

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

Question

Find the sum of the first 12 terms of the sequence.

1, -4, -9, -14, . . .

anonymous · Answer

You need to find the difference in each term and use the formula for the nth term. 
$$n_{th} = a_1+(n-1)d$$

anonymous · Answer

Since you need the sum of the first 12 terms you need to add them all up once you find them.

anonymous · Answer

The sum of that can also be done by a formula.

mathstudent55 · Answer

Most sequences we study are either arithmetic or geometric sequences.
Are you familiar with those terms?

anonymous · Answer

$$S_{n} =  \frac{ n(a_1+a_n) }{ 2 }$$
Where, 
n = the number of terms you are summing.
a1 = the first term.
an = the last term.

anonymous · Answer

d= 5 ?

anonymous · Answer

You can use the first formula to find the last term.

anonymous · Answer

Almost your numbers are negative.

anonymous · Answer

And yes, MathStudent

mathstudent55 · Answer

Ok, so you know this is a geometric sequence.
To find d, subtract any term from the next one.
For example, d = -9 - (-5) = -5

mathstudent55 · Answer

By adding the common difference, you can generate the next several terms. Then add them up to find the sum.
Of course, you can also use the formula @Johnbc gave you above.

anonymous · Answer

Thanks!

mathstudent55 · Answer

You're welcome.