What is f (x) = 2x - 4?

F (x) = 2x - 4 is rearrange to find the input, by letting f (x) = y, This is done by rearranging to y = 2x - 4, then add four: y + 4 = 2x and divide by 2 to make x the subject y + 4 / 2 = x now because the output of y becomes the input y + 4 / 2 = x becomes f^-1 (x) = x + 4 / 2