Answer:
y = 9 cos [(⅕pi)x]
Step-by-step explanation:
Amplitude = 9
Period = 10
2pi/10 = pi/5
I can’t see a picture of the grid
The given geometric series as shown in the question is seen to; Be converging with its' sum as 81
<h3>How to identify a converging or diverging series?</h3>
We are given the geometric series;
27 + 18 + 12 + 8 + ...
Now, we see that;
First term; a₀ = 27
Second Term; a₁ = 2(27/3)
Third term; a₂ = 2²(27/3²)
Fourth term; a₃ = 2³(27/3³)
Thus, the formula is;
2ⁿ(27/3ⁿ)
Applying limits at infinity gives;
2^(∞) * (27/3^(∞)) = 0
Since the terms of the series tend to zero, we can affirm that the series converges.
The sum of an infinite converging series is:
S_n = a/(1 - r)
S_n = 27/(1 - (2/3)
S_n = 81
Read more about converging or diverging series at; brainly.com/question/15415793
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The absolute value 
returns the "positive version" of a number.
In other words, if the number is positive, it remains positive; if the number is negative, it changes sign.
So, if we want 
, we want the "positive version" of x to be 9.
This can happen in two ways: if x is already 9, then its absolute value is still nine. If instead x=-9, its positive value will be 9 again.
In formula, we have
because
