domain is the numbes you are allowed to use for x
what I usually do is just find the numbers that aren't allowed in the domain. such numbers are numbers that cause a division by 0 or a squaer root of a negative number
given [tex]y=x^2[/tex], there are no numbers that you can use for x that will cause a division by 0 or a square root of a negative number
so domain is all real numbers or D={x | -∞<x<∞}
