Answer:

Step-by-step explanation:
Given
--- initial
-- rate
Value after a year = $20.70
Required
Expression to calculate its value after y years
This is calculated using:

Where

Substitute
in 



Substitute
and
in 

Step-by-step explanation:
<u>Step 1: Find the answer</u>



Answer: 
Using it's concept, the rate of change between point C and point D is of 2.
<h3>What is the average rate of change of a function?</h3>
The average rate of change of a function is given by the <u>change in the output divided by the change in the input</u>. Hence, over an interval [a,b], the rate is given as follows:

Considering the points of the given linear function, we have that:
Hence the rate of change between point C and point D is given by:
r = (4 - 2)/(2 - 1) = 2.
More can be learned about the average rate of change of a function at brainly.com/question/24313700
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Answer: (2, -25)
Step-by-step explanation:
The x coordinate of the vertex is
.
When x=2,
.
So, the vertex is (2, -25).
One reason that negative numbers would not make sense for values of the variables is that the solution having a negative value is not valid. It might be that the expression represents a real word problem and a negative value will not make any sense. Hope this helps.