**In
regular math books, this is called "substituting" or
"evaluating"... But, those are pretty big words
for something so easy.**

**
Check it out:**

**We are given something
like this:**

**And we need to find
what this thing equals when we put a number in for
x...
Like**

**
x = 3**

**Everywhere you see an
x...
stick in a
3!**

**What
about x =
-5?
We need to be careful with the negative! Use
(
)!**

**TRY IT:**

**Let x = 2:**

**Let x = -1:**