If f(x) and f-1(x) are inverse functions of each other and f(x)=2x+5, what is f-1(8)?

The correct option is [tex]B[/tex] and the value of [tex]f^{-1}(8)\;\rm{ is}[/tex] [tex]\frac{3}{2}[/tex].
Given: If [tex]f(x)[/tex] and [tex]f^{-1}(x)[/tex] are inverse functions of each other and [tex]f(x)=2x+5[/tex].
According to question:
[tex]f(x)=2x+5\\[/tex]
[tex]y=2x+5\\x=\frac{y-5}{2}\\[/tex]
[tex]f^{-1}(x)=\frac{x-5}{2}[/tex]
Now,
[tex]f^{-1}(8)=\frac{8-5}{2}\\f^{-1}(8)=\frac{3}{2}[/tex]
Hence, the value of [tex]f^{-1}(8)\;\rm{is}\;\frac{3}{2}[/tex].
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The required inverse of the function at when x = 8 is 3/2: Option B is correct
Given the function g(x)=2x+5, first we need to find the inverse of the function:
Let y = g(x)
y= 2x + 5
Replace y with x
x = 2y + 5
Make y the subject of the formula
2y = x - 5
y = (x - 5)/2
Hence the inverse of the expression is f^{-1}x = (x - 5)/2
Substitute x = 8 into the result
f^{-1}(8) = (8 - 5)/2
f^{-1}(8) = 3/2
Hence the required inverse of the function at when x = 8 is 3/2
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