The given equation is

If we replace x = 0, we have.

As you can observe, x = 0 satisfies the equation.
Therefore, zero is a solution of the given equation because when you replace it for the variable, you get a result that is true, that's why it's a solution.
If we get a result like 1 = 2, or 4 = 3, something false like that, then we have to conclude that it's not a solution. But, that's not the case here.