Answer:
[tex]f(12) = 323.02[/tex]
[tex]f(12) = 16.7 * 1.28^{12[/tex]
Step-by-step explanation:
Given
[tex]f(-2.5) = 9[/tex]
[tex]f(7) = 91[/tex]
[tex]f(12) = 16.7 * 1.28^{12[/tex]
Required
[tex]f(12)[/tex]
An exponential function is:
[tex]f(x) = ab^x[/tex]
[tex]f(-2.5) = 9[/tex] implies that:
[tex]9 = ab^{-2.5}[/tex]
[tex]f(7) = 91[/tex] implies that:
[tex]91 = ab^7[/tex]
Divide both equations
[tex]91/9 = ab^7/ab^{-2.5}[/tex]
[tex]91/9 = b^7/b^{-2.5}[/tex]
Apply law of indices
[tex]91/9 = b^{7+2.5}[/tex]
[tex]10.11 = b^{9.5}[/tex]
Take 9,5th root of both sides
[tex]b = 1.28[/tex]
So, we have:
[tex]9 = ab^{-2.5}[/tex]
[tex]9 = a * 1.28^{-2.5}[/tex]
[tex]9 = a * 0.54[/tex]
[tex]a = 9/0.54[/tex]
[tex]a = 16.7[/tex]
f(12) is calculated as:
[tex]f(x) = ab^x[/tex]
[tex]f(12) = 16.7 * 1.28^{12[/tex]
[tex]f(12) = 323.02[/tex]
