Question 706567
Since the inverse of each function will contain (y,x) for any (x,y) of the other function, we can identify two other points for the two points given.


f contains (2,-1), so the inverse of f will contain (-1,2) in addition to the already given (9,4).  We can now find the equation for {{{f^(-1)}}}.  Slope is {{{(9-(-1))/(4-2)}}} or m=5.  What about y intercept?  y=mx+b, b=y-mx, so pick a point;  b=4-5*9=-41.  so {{{f^(-1)=5x-41}}}.  Now you can find the original equation, f ?