Go to where 30 degrees is on the unit circle and find the y-coordinate. That is sin30.
Using it's vertex, the maximum value of the quadratic function is -3.19.
<h3>What is the vertex of a quadratic equation?</h3>
A quadratic equation is modeled by:

The vertex is given by:

In which:
Considering the coefficient a, we have that:
- If a < 0, the vertex is a maximum point.
- If a > 0, the vertex is a minimum point.
In this problem, the equation is:
y + 4 = -x² + 1.8x
In standard format:
y = -x² + 1.8x - 4.
The coefficients are a = -1 < 0, b = 1.8, c = -4, hence the maximum value is:

More can be learned about the vertex of a quadratic function at brainly.com/question/24737967
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X=9.3 is the answer to the question
Answer:
216
Step-by-step explanation:
I'm sure there is a simpler way to do this but this is how I did it.
First divide 18 by 6 because it triples every 6 hours.
18/6=3
This means it will triple three times
Then triple the value three times
#1. 8x3=24
#2. 24x3=72
#3. 72x3=216
In 18 hours the virus will infect 216 people.