Mathematics » Introducing Integers » Subtract Integers

Evaluating Variable Expressions with Integers

Evaluating Variable Expressions with Integers

Now we’ll practice evaluating expressions that involve subtracting negative numbers as well as positive numbers.

Example

Evaluate $$x-4\phantom{\rule{0.2em}{0ex}}\text{when}\phantom{\rule{0.2em}{0ex}}$$

1. $$\phantom{\rule{0.2em}{0ex}}x=3\phantom{\rule{0.2em}{0ex}}$$
2. $$\phantom{\rule{0.2em}{0ex}}x=-6.$$

Solution

To evaluate $$x-4$$ when $$x=3$$, substitute $$3$$ for $$x$$ in the expression.

 Subtract.

To evaluate $$x-4$$ when $$x=-6,$$ substitute $$-6$$ for $$x$$ in the expression.

 Subtract.

Example

Evaluate $$20-z\phantom{\rule{0.2em}{0ex}}\text{when}\phantom{\rule{0.2em}{0ex}}$$

1. $$\phantom{\rule{0.2em}{0ex}}z=12\phantom{\rule{0.2em}{0ex}}$$
2. $$\phantom{\rule{0.2em}{0ex}}z=-12$$

Solution

To evaluate $$20-z\phantom{\rule{0.2em}{0ex}}\text{when}\phantom{\rule{0.2em}{0ex}}z=12,$$ substitute $$12$$ for $$z$$ in the expression.

 Subtract.

To evaluate $$20-z\phantom{\rule{0.2em}{0ex}}\text{when}\phantom{\rule{0.2em}{0ex}}z=-12,\phantom{\rule{0.2em}{0ex}}\text{substitute}\phantom{\rule{0.2em}{0ex}}-12\phantom{\rule{0.2em}{0ex}}\text{for}\phantom{\rule{0.2em}{0ex}}z\phantom{\rule{0.2em}{0ex}}\text{in the expression.}$$

 Subtract.