I can prove it cannot be anything else. The only way to make you see that is use geometry, sorry, with the hope of being able to appeal to your intution. Final shot, then I am out
Consider the equation x = x/10. We already know that zero is a solution because 0/10 = 0. But is that solution unique?
Let's go back to my two straight lines with cartesian equations:
y = x
y = x/10
If you take an xy cartesian plane and plot various points that satisfy these equations, you will immediately see that they represent two different and not parallel straight lines.
How do we find the intersection, if any? We impose that the y coordinate is the same, for instance. That is a necessary condition for intersection.
Ths leads to our initial equation:
x = x/10
Does that have at least one solution? Yes, zero. We know that. So, if we plug in zero in the x of both equation we get the same y. It cannot be otherwise, since we imposed that condition.
So, x = 0 and y = 0 satisfy both equations of the two lines. As it can be easily verified. It is their intersection.
And what is the number of intersections of two non parallel straight lines (remember Euclid)? One, of course.
Therefore, the solution is unique. Non parallel straight lines on the plane meet at one and only one point. Which entails that the solution of x = x/10 is unique (otherwise you get two different intersections for the same y) and can only be zero. The known solution.
So, any number that is equal to itself when divided by 10 can only be zero. And if 0.000...1 satisfies this property, then 0.00...1 can only be equal to zero. Ergo the difference between 1 and 0.9999... Is zero. And so, 1 = 0.9999....
Ciao
- viole