The domain is all reals; x can take any real value.

How do you work this out? Well, you start by asking yourself "are there any points or regions at which the function is undefined?" Since the function is a rational function (i.e. a fraction), an obvious place to start is by asking yourself forwhat values of x will the denominator be zero(and cause a problem)?

But a quick glance at the denominator should tell you that the denominator can never be zero for any value of x; specifically, the denominator is always 2 or higher.

Now, for any other possible points at which the function becomes undefined, note that there is a square root. Since we're considering only real numbers, recall that we cannot find the square root of a negative number. So you should now ask yourselffor what values of x is x^2 + 4 < 0? The answer is none. So the square root doesn't cause any problems in the function.

So there are no values of x such that the function will become undefined, and therefore the domain of the function is all reals.

Hope this helps.

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