When finding the domain of a function, you want to exclude those values of x which cause the function to be undefined (division by zero) or have complex values (an even root of a negative value). There are also restrictions on logarithmic and inverse trigonometric functions as well.
Polynomial functions such as the first two, have no restrictions on the domain as there is no division or radicals. For the remaining three, set the expressions under the radicals greater than or equal to zero, and solve for x. This will tell you the valid values for x, which is the domain of the function. What do you find?
Just take the expression under the radical, and state that it is greater than or equal to zero. For example, doing this for the third one gives:
$\displaystyle x-60\ge0$
Now add 60 to both sides, and what does this tell you about $\displaystyle x$?
No, there is no upper bound so we use $\displaystyle \infty$ as the upper bound. So for the third one you would write:
$\displaystyle 60\le x\le\infty$
What did you write for the first two since there is no lower or upper bounds?