The graph is an illustration of an exponential function
The true statement is (d) [tex]\mathbf{f(n) = 4(3)^{n-1}}[/tex], [tex]\mathbf{f(5) = 324}[/tex]
An exponential function is represented as:
[tex]y = ab^{x-1}[/tex]
From the graph, we have the following points
[tex](x_1,y_1) = (1,4)[/tex]
[tex](x_2,y_2) = (2,12)[/tex]
So, we have:
[tex]y = ab^{x-1}[/tex] --------- [tex](x_1,y_1) = (1,4)[/tex]
[tex]4 = ab^{1-1}[/tex]
[tex]4 =ab^0[/tex]
[tex]4 =a \times 1[/tex]
[tex]4 =a[/tex]
[tex]a = 4[/tex]
[tex]y = ab^{x-1}[/tex] --------- [tex](x_2,y_2) = (2,12)[/tex]
[tex]12 = ab^{2-1[/tex]
[tex]12 = ab[/tex]
Substitute [tex]a = 4[/tex]
[tex]12 = 4b[/tex]
Divide both sides by 4
[tex]3 = b[/tex]
[tex]b =3[/tex]
Recall that:
[tex]y = ab^{x-1}[/tex]
So, we have::
[tex]y = 4(3)^{x-1}[/tex]
Express as a function of n
[tex]\mathbf{f(n) = 4(3)^{n-1}}[/tex]
Substitute 5 for n, to calculate the 5th term
[tex]\mathbf{f(5) = 4(3)^{5-1}}[/tex]
[tex]\mathbf{f(5) = 4(3)^4}[/tex]
[tex]\mathbf{f(5) = 324}[/tex]
Hence, option (d) is correct
Read more about exponential functions as:
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