## Evaluate a 1-Variable Expression

### Evaluate Expressions: Learn

A mathematic *expression* is a group of numbers and
operators which can be evaluated to determine their value.

There may be a *variable* in the expression which
represents a number that may or may not be known. A variable
is simply a symbol used as a placeholder for the unknown
number. Mathematicians frequently use "x" as the variable,
but it could be anything, such as any letter of the alphabet,
or even a smiley face drawing.

If we know the value of the variable, we can find the value of the entire expression.

For example, if x=3, then the expression 7x+4 can be evaluated in the following way:

7x+4 =7*3+4 =21+4 =25

The very first step where x is replaced by its value is called
*substitution*.

### Evaluate Expressions: Practice

#### Evaluate using the given value.

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If x=, then

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