Question

For which function is f(x) equal to f-1(x)?

Answer 1

C...to show this, interchange letters: x = (y+1)/(y-1)xy-x = y + 1xy - y) = x + 1y(x-1) = x+1y = (x+1)/(x-1) ⇐ this is f-1(x) and it's identical to f(x).  Note: the equal sign is missing in the definitions of the functions c. & d.