Problem 36 - College Algebra

Question

In Exercises 27–62, graph the solution set of each system of inequalities or indicate that the system has no solution. $$\left\\{\begin{array}{l} x \leq 3 \\ y \leq-1 \end{array}\right.$$

Step-by-Step Solution

Answer

The solution to the system of inequalities is the region of the graph that is below the line \(y = -1\) and to the left of the line \(x = 3\).

Step 1: Graph the first inequality

The inequality \(x \leq 3\) is drawn on the graph. This is a vertical line that passes through the point (3,0). The line is solid because the inequality includes 'or equal to'. All points to the right of this line will satisfy the inequality.

Step 2: Graph the second inequality

Next, draw the inequality \(y \leq -1\). This will be a horizontal line passing through the point (0,-1). Again, use a solid line because it includes 'or equal to'. All points below this line will satisfy the inequality.

Step 3: Identify the solution set

The common area which satisfies both inequalities is the solution set. It will be the part of the graph that is lower than the line \(y = -1\) and to the left of the line \(x = 3\). So all points in this area, including points on the boundary lines, will be a solution to the system of inequalities.

Key Concepts

Solving Inequalities

Inequality problems can seem daunting at first, but with a systematic approach, they become much easier to understand. To solve an inequality means to find all the possible values that can satisfy the condition given by the inequality. Inequalities differ from equations in that they can have a range of solutions, rather than a single value. Imagine it as finding the possible range where you can step on a number line rather than just one spot to stand.

The key is to treat the inequality sign just like an equal sign when performing arithmetic operations, with one important exception: if you multiply or divide by a negative number, you must reverse the inequality sign. This critical step ensures that the relative size of each side of the inequality remains true. For example, if we have the inequality \(3x < 12\), when we divide both sides by 3, we get \(x < 4\), which means any number less than 4 is a solution to the inequality.

Inequality Graphing

Visualizing inequalities on a graph can be incredibly helpful for understanding the set of solutions. When graphing inequalities, the type of line used is very important. A solid line indicates that the boundary is part of the solution set, meaning the relation includes 'equal to.' Dashed lines are used when the boundary isn't included – in other words, when the inequality does not include the 'equal to.' Most importantly, always remember to shade the area that represents the solutions.

For one-variable inequalities, like \(x \leq 3\), you'll shade the entire side of the graph that corresponds to numbers less than or equal to 3. Similarly, for \(y \leq -1\), you'll shade downwards because all the y-values that satisfy the inequality are below or at -1 on the y-axis. The shaded region of the graph becomes a visual representation of all the acceptable solutions.

System of Inequalities Solution

When deciding where to shade for a system of inequalities, a good place to start is by graphing each inequality separately, as you've learned previously. After graphing, it's the overlap or intersection of these shaded areas that is the true solution set for the system. In our example, we have two simple inequalities that give us two separate shaded areas: the area to the left of \(x = 3\) and the area below \(y = -1\).

The solution to the system is where these shaded areas intersect, which visually can be imagined as the 'overlap' on the graph. In simple terms, the coordinates that fall within both individual solution sets satisfy the system. This is why graphing inequalities can be much more insightful than just solving algebraically – it allows students to 'see' the answer.

Algebraic Graph Analysis

The last step usually involves analyzing the graph from an algebraic standpoint. This is where you take the visual representation and interpret what it means for the values that you can choose for the variables. It’s like you’re reading a map that tells you where you can go. For a system like ours, the algebraic analysis would tell us that any pair of numbers \(x,y\) where \(x \leq 3\) and \(y \leq -1\) would work as a solution.

While graphing gives us the 'where' visually, algebra gives us the 'why' and the 'how' to express our solutions in terms of inequalities or solution sets. For instance, the solution to our system can be described algebraically as all ordered pairs \(x, y\) such that \(x \leq 3\) and \(y \leq -1\). Learning to switch between the visual graph and the algebraic expression is key to mastering graph analysis.