a) For the domain we usually look for where x is not defined. So do you know of any values of x where does not exist?

b)

Now, sketch a right triangle with hypotenuse of length 1. (We can actually choose any length we like for this. I choose 1 as a standard) and let one of the non-right angles be . My typical orientation is that the hypotenuse slopes up and to the right, and my is in the lower left corner. Define . This means that . So we know that the legs of the right triangle (x and y in an obvious orientation) are related by

So the Pythagorean theorem says that

So

and

So finally:

c) This is virtually identical to b). In fact, the right triangle is exactly the same, it's just that instead of 5 you have an x. (You'll want to change the variables x and y that I used in the above derivation, of course.)

-Dan