Compound inequalities are mathematical expressions that involve two or more inequalities combined into a single statement. These inequalities are crucial in representing ranges of values on a number line or a graph. When interpreting graphs of compound inequalities, it is essential to understand how these inequalities are expressed and what the graph visually represents. This article delves into the concept of compound inequalities, explains how to interpret their graphs, and provides a comprehensive understanding of how to determine which compound inequality is represented by a given graph.

**Understanding Compound Inequalities**

Compound inequalities consist of two or more inequalities joined by the words “and” or “or.” These conjunctions define how the solution sets of the individual inequalities interact.

- Conjunction (“And”)

When two inequalities are combined with “and,” the solution set includes values that satisfy both inequalities simultaneously. The graph of a compound inequality using “and” is typically the intersection (overlap) of the solution sets of the individual inequalities.

**Example**: x>2x > 2x>2 and x<5x < 5x<5

This compound inequality can be written as 2<x<52 < x < 52<x<5.

The solution set includes all values of xxx that are greater than 2 and less than 5.

The graph is a segment on the number line between 2 and 5, not including the endpoints.

- Disjunction (“Or”)

When two inequalities are combined with “or,” the solution set includes values that satisfy either of the inequalities. The graph of a compound inequality using “or” is the union of the solution sets of the individual inequalities.

**Example**: x≤−1x \leq -1x≤−1 or x≥3x \geq 3x≥3

The solution set includes all values of xxx that are less than or equal to -1 or greater than or equal to 3.

The graph consists of two rays: one starting at -1 and extending leftward, and the other starting at 3 and extending rightward.

**Interpreting the Graph of a Compound Inequality**

To determine which compound inequality is represented by a graph, follow these steps:

**Identify the critical points** on the number line where the inequalities change.

**Determine whether the critical points are included** in the solution set (closed circles) or excluded (open circles).

**Observe the direction** of the shading on the number line to understand which ranges are included in the solution set.

**Combine the inequalities** using “and” or “or” based on whether the shading overlaps (and) or is separate (or).

Example 1: Compound Inequality with “And”

Consider a graph with shading between -3 and 2, with open circles at both -3 and 2.

**Step 1**: The critical points are -3 and 2.

**Step 2**: Both critical points are excluded (open circles).

**Step 3**: The shading is between -3 and 2.

**Step 4**: Combine the inequalities.

The graph represents the compound inequality −3<x<2-3 < x < 2−3<x<2.

Example 2: Compound Inequality with “Or”

Consider a graph with shading to the left of -2 (including -2) and shading to the right of 3 (including 3).

**Step 1**: The critical points are -2 and 3.

**Step 2**: Both critical points are included (closed circles).

**Step 3**: The shading is to the left of -2 and to the right of 3.

**Step 4**: Combine the inequalities.

The graph represents the compound inequality x≤−2x \leq -2x≤−2 or x≥3x \geq 3x≥3.

Graphing Compound Inequalities

To graph compound inequalities, follow these steps:

**Graph each individual inequality** on the same number line.

**For “and” compound inequalities**, identify the intersection (overlapping region) of the individual graphs.

**For “or” compound inequalities**, identify the union (combined regions) of the individual graphs.

**Use open or closed circles** to indicate whether endpoints are included or excluded.

**Practical Applications of Compound Inequalities**

Compound inequalities are used in various fields to represent ranges and conditions. Here are some practical applications:

- Economics

In economics, compound inequalities can represent ranges of acceptable prices, wages, or quantities. For example, a company may need to keep production costs between certain limits to remain profitable.

**Example**: 50<P<10050 < P < 10050<P<100 (where PPP is the price of a product)

- Environmental Science

Environmental regulations often specify acceptable ranges for pollutant levels. Compound inequalities can represent these permissible limits.

**Example**: 0≤x≤100 \leq x \leq 100≤x≤10 (where xxx is the concentration of a pollutant in parts per million)

- Medicine

In medicine, compound inequalities can describe safe dosage ranges for medications. Patients must receive doses within a specific range to be effective and safe.

**Example**: 5 mg≤D≤20 mg5 \, \text{mg} \leq D \leq 20 \, \text{mg}5mg≤D≤20mg (where DDD is the dosage of a drug)

**Conclusion**

Understanding which compound inequality is represented by a graph involves recognizing the critical points, determining inclusion or exclusion of these points, observing the direction of shading, and combining inequalities with “and” or “or.” By mastering these concepts, one can accurately interpret and represent compound inequalities in various practical applications.

Whether in mathematics, economics, environmental science, or medicine, compound inequalities provide a powerful tool for describing ranges and conditions. Through careful analysis and interpretation, we can use these inequalities to solve real-world problems and make informed decisions.