Evaluate [latex]x+7[/latex] when

1. [latex]x=3[/latex]
2. [latex]x=12[/latex]

Answer: Solution: 1. To evaluate, substitute [latex]3[/latex] for [latex]x[/latex] in the expression, and then simplify.

	[latex]x+7[/latex]
Substitute.	[latex]\color{red}{3}+7[/latex]
Add.	[latex]10[/latex]

When [latex]x=3[/latex], the expression [latex]x+7[/latex] has a value of [latex]10[/latex]. 2. To evaluate, substitute [latex]12[/latex] for [latex]x[/latex] in the expression, and then simplify.

	[latex]x+7[/latex]
Substitute.	[latex]\color{red}{12}+7[/latex]
Add.	[latex]19[/latex]

When [latex]x=12[/latex], the expression [latex]x+7[/latex] has a value of [latex]19[/latex]. Notice that we got different results for parts 1 and 2 even though we started with the same expression. This is because the values used for [latex]x[/latex] were different. When we evaluate an expression, the value varies depending on the value used for the variable.

[latex]\text{Evaluate }3x+4y - 6\text{ when }x=10\text{ and }y=2[/latex].

Answer: SolutionThis expression contains two variables, so we must make two substitutions.

	[latex]3x+4y-6[/latex]
Substitute [latex]\color{red}{10}[/latex] for x and [latex]\color{blue}{2}[/latex] for y.	[latex]3(\color{red}{10})+4(\color{blue}{2})-6[/latex]
Multiply.	[latex]30+8-6[/latex]
Add and subtract left to right.	[latex]32[/latex]

When [latex]x=10[/latex] and [latex]y=2[/latex], the expression [latex]3x+4y - 6[/latex] has a value of [latex]32[/latex].