High School

If [tex]f(x)[/tex] is an exponential function of the form [tex]y = ab^x[/tex], where [tex]f(4.5) = 17[/tex] and [tex]f(5) = 94[/tex], find the value of [tex]f(7)[/tex] to the nearest hundredth.

Answer :

We start with the exponential function

[tex]$$
f(x) = a b^x,
$$[/tex]

and we are given that

[tex]$$
f(4.5) = a\, b^{4.5} = 17 \quad \text{and} \quad f(5) = a\, b^5 = 94.
$$[/tex]

Step 1. Eliminate [tex]\(a\)[/tex] to find [tex]\(b\)[/tex]:

Divide the second equation by the first:

[tex]$$
\frac{a\, b^5}{a\, b^{4.5}} = \frac{94}{17}.
$$[/tex]

This simplifies to

[tex]$$
b^{5-4.5} = b^{0.5} = \frac{94}{17}.
$$[/tex]

Squaring both sides to solve for [tex]\(b\)[/tex],

[tex]$$
b = \left(\frac{94}{17}\right)^2.
$$[/tex]

Step 2. Solve for [tex]\(a\)[/tex]:

Use the equation for [tex]\(f(4.5)\)[/tex]:

[tex]$$
a\, b^{4.5} = 17.
$$[/tex]

Thus,

[tex]$$
a = \frac{17}{b^{4.5}}.
$$[/tex]

Step 3. Find [tex]\(f(7)\)[/tex]:

We substitute into the function:

[tex]$$
f(7) = a\, b^7.
$$[/tex]

Using our expression for [tex]\(a\)[/tex] we can write:

[tex]$$
f(7) = \frac{17}{b^{4.5}} \, b^7 = 17 \, b^{7-4.5} = 17 \, b^{2.5}.
$$[/tex]

Upon calculating the numerical value, we obtain

[tex]$$
f(7) \approx 87870.59810107638.
$$[/tex]

Rounding to the nearest hundredth, we have

[tex]$$
f(7) \approx 87870.60.
$$[/tex]

Thus, the value of [tex]\(f(7)\)[/tex] is

[tex]$$
\boxed{87870.60}.
$$[/tex]