what is 9+10

$${\mathtt{10}}{\mathtt{\,\small\textbf+\,}}{\mathtt{9}} = {\mathtt{19}} = \tiny\text{Error: }$$

Let x=y.
We can multiply each side by y to get:

Subtract x^2 from both sides to get:

Factor each side to get:

The common factors of (y - x) cancel out to get:

Given that y = x, we can conclude that:

And so therefore:

Thus:

So:

And:

Then:

Finally: