Robin bought a computer for $1,250. it will depreciate, or decrease in value, by 10% each year that she owns it. a) is the sequence formed by the value at the beginning of each year arithmetic, geometric, or neither? explain. b) write an explicit formula to represent the sequence. c) find the value of the computer at the beginning of the 6th year.

Remember that the general formula of geometric sequence is 
where 
is the nth term
is the difference
is the place of the term in the sequence
Also, to find  we will use the formula: 
where 
is the current term in the sequence 
is the previous term 

a) Lets find the three first terms of our sequence to check what type of sequence we have:
We know for our problem that the initial value of the computer is $1250, so our first term is 1250. In other words .
To fin our second term , we are going to subtract 10% of the value to our original value:
and , so 

To find our third term  we are going to subtract yet again 10% to our current value:
and , so

Now that we have our sequence  lets check if we have a consistent  to prove we have a geometric sequence:
- with , and :
  
- with , and :
  
Look! our s are the same, so we can conclude that we have a geometric sequence.

b) To do this we just need to replece the values of our sequence in the general formula of a geometric sequence. We know from our previous point that  and . So lets replace those values in geometric sequence formula to find our explicit formula:


c) To find the value of the computer at the beginning of the 6th year, we just need to find the 6th therm in our geometric sequence:




We can conclude that the value of the computer at the beginning of the 6th year will be $738.1125

We want to answer different things about an exponential decay, the answers are:

a) Geometric.b) c) $738.10.

So we know that the original price of the computer is $1250 and the value decays by 10% each year.

So in year 1, the new value of the computer will be:

V = $1250*(1 - 0.1) = $1250*0.9

On year 2, the new value will be:

V = ( $1250*0.9)*0.9 = $1250*(0.9)^2

And so on.

a) This sequence is a geometric sequence because each term is a constant times the previous term, where the constant is 0.9.

b) The explicit formula for a geometric sequence is:

where:

k is the constant, in this case, is 0.9

A1 is the first term of the sequence, in this case, is 1250

Then we have:

c) Here we just need to replace n by 6 in the above formula:

This means that the price of the computer in the 6th year is $738.10

If you want to learn more about exponential decays, you can read:

link

The correct answer is addition

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