Assuming x is your input, then yes.
A function means every input (x) has only one output (y).
In x=10, every single input has an output of 10, but don't be fooled.
Think about it, for any x you input, there is only one output (10).
On the other hand, the output (10) has multiple inputs for it. However, this still obeys the rule that every input has only one output.
In conclusion, x=10 is, technically, a function.
Another way to test this is to plot points following the equation on a graph, draw a line for them, and do what's called the "vertical line test."
For x=10 to be a function, you must be able to draw a straight vertical line for every x value on the graph, and only hit the line for the points ONCE. If anywhere on the graph, there is a spot that you can draw a vertical line on the graph and it hits two or more points on the line for your points, then the equation is not a function.
When graphing x=10 and conducting the vertical line test, the result is that x=10 IS a function.
