Question

Given the function f(x) = 3x, find the value of f−1(81).

f−1(81) = 1

f−1(81) = 2

f−1(81) = 3

f−1(81) = 4

Answer 1

First find the inverse of 3x, know how?

Answer 2

To find the inverse:

Replace f(x) with y
Switch x's and y's, so put x where y is and x where y is.
Solve for y
Replace y with f^-1(x)

Answer 3

@D3xt3R

Answer 4

@bribri50 is \[f(x)=3^x~~or~~3x\]??

Answer 5

you are being asked to solve
\[3^x=81\] for \(x\)
it should be more or less obvious

Answer 6

@D3xt3R look at the answers:)

Answer 7

\[f(x)=3^x\]
\[x=3^{f(x)}\]
\[f^{-1}(x)=log_3(x)\]
\[f^{-1}(81)=log_3(81)\]
\[f^{-1}(81)=log_3(3^4)\]
\[\boxed{f^{-1}(81)=4}\]

Answer 8

Oh given the options, that makes much more sense!

Answer 9

;D