Three million twenty nine and two hundred fifty one
Answer:
A.
Step-by-step explanation:
Take a look at what happens when squaring either of these...

Notice a couple of patterns.
1. The last term has a positive coefficient. That rules out answer choices C and D.
2. The coefficient of the middle term is either
. So what are <em>a</em> and <em>b</em>? <em>a</em> is the square root of the x^2 term and <em>b</em> is the square root of the y^2 term.

The middle coefficient needs to be either +30 or -30. The answer is choice A.
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
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