Using a geometric sequence, it is found that:
a) The explicit formula is: [tex]a_n = 250000(2.1)^{n-1}[/tex].
b) The value of her collection 9 years after she started tracking is of $94,557,148.
What is a geometric sequence?
A geometric sequence is a sequence in which the result of the division of consecutive terms is always the same, called common ratio q.
The nth term of a geometric sequence is given by:
[tex]a_n = a_1q^{n-1}[/tex]
In which [tex]a_1[/tex] is the first term.
Item a:
Three years ago, her collection was worth $250,000, hence the first term is [tex]a_1 = 250000[/tex].
In two years, the collection was valued at $1,102,500, hence the common ratio is:
[tex]q^2 = \frac{1,102,500}{250,000}[/tex]
[tex]q^2 = 4.41[/tex]
[tex]q = \sqrt{4.41} = 2.1[/tex].
Hence, the explicit formula is:
[tex]a_n = 250000(2.1)^{n-1}[/tex]
Item b:
[tex]a_9 = 250000(2.1)^{9-1} = 94557148[/tex]
The value of her collection 9 years after she started tracking is of $94,557,148.
More can be learned about geometric sequences at https://brainly.com/question/11847927