# How do you find the domain of #f(x) =sqrt(9 - x)#?

##### 1 Answer

To find the (real) domain, we need to make sure we

(1) don't try to take even roots of negative numbers (square roots, 4th, 6th, 8th and so on)

(2) don't try to divide by zero

(and more rarely avoid other undefined expressions like

For

We need to make sure that

So we need to make sure that

Solve:

(I prefer to avoid negatives in front of the

Let's make it look like what it ays, by writing it this way:

all (real) numbers,

There are other ways of expressing the answer, but they all refer to the same set of numbers"

**Final note**

It may seem or 'feel' a little odd that we could use, for example,

Before we take the square root, we're going to find

We could not use