Answer:
Explained below.
Step-by-step explanation:
Consider the series is a set of first 6 natural numbers.
Sum of first <em>n</em> terms is:



Consider the series is an arithmetic sequence.
Sum of first <em>n</em> terms is:
![S_{n}=\frac{n}{2} [2a+(n-1)d]](https://tex.z-dn.net/?f=S_%7Bn%7D%3D%5Cfrac%7Bn%7D%7B2%7D%20%5B2a%2B%28n-1%29d%5D)
Here<em>,</em>
<em>a</em> = first term
<em>d</em> = common difference
Consider the series is an geometric sequence.
Sum of first <em>n</em> terms is:

Here<em>,</em>
<em>a₁</em> = first term
<em>r</em> = common ratio
Answer:
-18
Step-by-step explanation:
-12 + (-2)(3)
= (-12)+((-2)x(3))
= (-12)+(-6)
= (-12)-(6)
= -18