Solution
Remember [latex]ab[/latex] means [latex]a[/latex] times [latex]b[/latex], so [latex]9x[/latex] means [latex]9[/latex] times [latex]x[/latex].
1. To evaluate the expression when [latex]x=5[/latex], we substitute [latex]5[/latex] for [latex]x[/latex], and then simplify.

2. To evaluate the expression when [latex]x=1[/latex], we substitute [latex]1[/latex] for [latex]x[/latex], and then simplify.

Notice that in part 1 that we wrote [latex]9\cdot 5[/latex] and in part 2 we wrote [latex]9\left(1\right)[/latex]. Both the dot and the parentheses tell us to multiply.

1. Substitute 0 for [latex]x[/latex].
   [latex]\begin{array}{ll}2x+7 \hfill& = 2\left(0\right)+7 \\ \hfill& =0+7 \\ \hfill& =7\end{array}[/latex]
2. Substitute 1 for [latex]x[/latex].
   [latex]\begin{array}{ll}2x+7 \hfill& = 2\left(1\right)+7 \\ \hfill& =2+7 \\ \hfill& =9\end{array}[/latex]

Solution
We substitute [latex]10[/latex] for [latex]x[/latex], and then simplify the expression.

When [latex]x=10[/latex], the expression [latex]{x}^{2}[/latex] has a value of [latex]100[/latex].

Solution
In this expression, the variable is an exponent.

When [latex]x=5[/latex], the expression [latex]{2}^{x}[/latex] has a value of [latex]32[/latex].

Solution

This expression contains two variables, so we must make two substitutions.

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

Solution
We need to be careful when an expression has a variable with an exponent. In this expression, [latex]2{x}^{2}[/latex] means [latex]2\cdot x\cdot x[/latex] and is different from the expression [latex]{\left(2x\right)}^{2}[/latex], which means [latex]2x\cdot 2x[/latex].