Question

Model 3xfx Write the inverse of the rational function used to represent the situation in model 3, .

A biologist has tracked the population of Antarctic penguins in a marine reserve since 2012. He represents the population with the rational function f(x)=15x+50/x+5, where is the number of years that have passed since 2012 and () is the number of penguins.

Answer 1

Make f(x) = y
y = (15x + 50)/(x + 5)
Swap the x and y and make y the subject again
x = (15y + 50)/(y + 5)
x(y + 5) = 15y + 50
xy + 5x = 15y + 50
xy - 15y = 50 - 5x
y(x - 15) = 50 - 5x
y = (50 - 5x)/(x - 15)
So inverse function f^-1(x) = (50 - 5x)/(x - 15)