Question 1039984
f(x)=(6-x)/(3+4x)
x=(6-y)/(3+4y), interchange x and y
3x+4xy=6-y
y+4xy=6-3x
y(1+4x)=6-3x
y=f inv (x)=(6-3x)/(1+4x)
domain of original function is all x except -(1/4)
domain of inverse function is all x except x=(-1/4)
f(3)=3/15=1/5
f inv (1/5)=(6-3/5)/(1+4/5)
This is 27/5/9/5, or 3.
Notice how it gives the original f(3) result back.
{{{graph(300,200,-10,10,-10,10,(6-x)/(3+4x),(6-3x)/(1+4x))}}}  Notice the symmetry around the line y=x.