Answer: Choice A
S9 = (9/2)*(2+26)
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The formula is
Sn = (n/2)*(a1+an)
where
Sn = sum of the first n terms (nth partial sum)
n = number of terms
a1 = first term
an = nth term
In this case,
n = 9
a1 = 2 (plug in n = 1 into the formula an = 3n-1 and simplify)
an = a9 = 26 (plug n = 9 into the formula an = 3n-1 and simplify)
So,
Sn = (n/2)*(a1+an)
S9 = (9/2)*(2+26)
will help us find the sum of the first 9 terms of this arithmetic sequence
Narrowing it down it's either a or c because the other 2 choices open downward (negative a).
Graphing the 2 parabolas choice c is narrower.
c
The answer would be -9.72
The length of the radius of circle o is 18 cm.
<h2>
</h2><h2>
Given that</h2>
Circle o has a circumference of 36π cm.
<h3>
We have to determine</h3>
What is the length of the radius, r?
<h3>According to the question</h3>
Circle o has a circumference of 36π cm.
The length of the radius of the circle is determined by the following formula;

Substitute all the values in the formula;

Hence, the length of the radius of circle o is 18 cm.
To know more about Circumference click the link given below.
brainly.com/question/4268218
Answer:

Step-by-step explanation:
you have to use the midpoint formula which is

so you plug your numbers in

Add the tops

if possible simplify
and that is your answer