The graphs of a function \(f(x)=3x+b\) and its inverse function \(f^{-1}(x)\) intersect at the point \((-3,a)\). Given that \(b\) and \(a\) are both integers, what is the value of \(a\)?

Guest Feb 17, 2019

#1**+1 **

\(\text{if }v=f(u) \text{ then } u = f^{-1}(v) \text{ in other words}\\ \text{if }(u,v) \text{ is a point on }f(u) \text{ then }(v,u) \text{ must be a point on }f^{-1}(v)\\ \text{thus if these two points are identical}\\ (u,v)=(v,u) \Rightarrow u=v\)

\(\text{so if }(-3,a) \text{ is on the graph of }f(x)\\ (a,-3) \text{ is on the graph of }f^{-1}(x) \\ \text{and if they coincide then }a=-3\)

.Rom Feb 17, 2019