Write down in as a word .two million one hundred and five thousand two hundred and six

2,105,206 is two million one hundred and five thousand two hundred and six.

Depends greatly on the type of function.
Some things to keep in mind:
1.) the value of the denominator of a fraction cannot be zero
2.) the inside of an even root cannot be less than zero
3. The argument of a logarithmic function must be greater than zero
4. Plus many more other rules and such

But a simpler explanation, just find out what values x can be for the given function, and what y can be.
The x values make up the domain, the y, the range

Graphs are helpful
Hope this helps!