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If f ( x ) f(x) is an exponential function where f ( − 3.5 ) = 25 f(−3.5)=25 and f ( 6 ) = 33 f(6)=33, then find the value of f ( 6.5 ) f(6.5), to the nearest hundredth.

Sagot :

Given:

f(x) is an exponential function.

[tex]f(-3.5)=25, f(6)=33[/tex]

To find:

The value of f(6.5).

Solution:

Let the exponential function is

[tex]f(x)=ab^x[/tex]         ...(i)

Where, a is the initial value and b is the growth factor.

We have, [tex]f(-3.5)=25[/tex]. So, put x=-3.5 and f(x)=25 in (i).

[tex]25=ab^{-3.5}[/tex]         ...(ii)

We have, [tex]f(6)=33[/tex]. So, put x=6 and f(x)=33 in (i).

[tex]33=ab^{6}[/tex]         ...(iii)

On dividing (iii) by (ii), we get

[tex]\dfrac{33}{25}=\dfrac{ab^{6}}{ab^{-3.5}}[/tex]

[tex]1.32=b^{9.5}[/tex]

[tex](1.32)^{\frac{1}{9.5}}=b[/tex]

[tex]1.0296556=b[/tex]

[tex]b\approx 1.03[/tex]

Putting b=1.03 in (iii), we get

[tex]33=a(1.03)^{6}[/tex]

[tex]33=a(1.194)[/tex]

[tex]\dfrac{33}{1.194}=a[/tex]

[tex]a\approx 27.63[/tex]

Putting a=27.63 and b=1.03 in (i), we get

[tex]f(x)=27.63(1.03)^x[/tex]

Therefore, the required exponential function is [tex]f(x)=27.63(1.03)^x[/tex].