P is equal to 29. You take the question backwards: 12*3 then subtract 7
The answer is an equation, a condition:
f(x) = f^(-1)(x), then apply f(x) again: f(f(x) ) = f(f^-1(x)) = x,
f(f(x)) =x, that means that:
The point of intersection is the point where applying f(x) twice it results in the identity. A similar argument takes you to f^(-1)(f^(-1)(x)) = x.
Furthermore, the final answer is the point where f(x)=x (which coincides with f^(-1)(x)=x). That is the value of x where the function crosses the line y=x. If there is no such point, then f(x) and f^(-1)(x) will never cross each other.
I can see the proof graphically, so I can't post it.
For a line, it always works:
f(x) = ax+b, f^(-1)(x) = (x-b)/a, ax+b = (x-b)/a --> a^2x+ab=x-b,
x = -(a+1)*b/(a^2-1) = -b/(a-1). Which is indeed where f(x)=x.
