I am just trying the hello world code piece. I find that if the input number is bigger, the relationship between x and y are not quite linear. Anyone knows why?

If the input is 10, its output is around 19. But if the input is 10000000, the output doesn’t show result that is near what you get from y=2x-1. Does that mean the x and y relationship guessed by the neural network is actually not y=2x-1, but something else. I mean how do we know what kind of formulas the network get?