Presentation on theme: "Sections 5.1 & 5.2 Inequalities in Two Variables"— Presentation transcript:
1 Sections 5.1 & 5.2 Inequalities in Two Variables After today’s lesson, you will be able tograph linear inequalities in two variables.solve systems of linear inequalities.solve applications of linear inequalities in two variables.
2 Half-PlanesA line divides the plane into two regions called half-planes.A vertical line divides it into left and right half planes.A nonvertical line divides it into upper and lower half-planes.In either case, the dividing line is called the boundary line of each half plane, as indicated in the figure.Boundary LineUpper Half-planeLeft half-planeRight half-planeLower Half-planeBoundary Line
3 Strategy For Graphing Linear Inequalities Express the inequality in slope-intercept form (if it is not a vertical line.)Graph the related equation as the boundary line.If the symbol is < or > , draw the line dotted.If the symbol is or , draw the line solid.
4 Strategy For Graphing Linear Inequalities Choose a test point on either side of the boundary line. The point (0, 0) is a good choice, if it is not on the boundary line. Substitute the values of x and y into the original inequality.If the statement is TRUE, shade the half-plane containing the test point.If the statement is FALSE, shade the half-plane NOT containing the test point (the opposite side).
5 Strategy For Graphing Linear Inequalities Notice, for equations in slope-intercept form:If y < or y , shade below the line.If y > or y , shade above the line.Label the equation of the boundary line (use an = sign) and label the test point.
6 Graphing a Linear Inequality Example 1 Example 1: Graph the linear inequalityyx
7 Graphing on the Calculator LineA straight line or curved graph is shown Y1 =AboveShading covers the area above a graphY1 =BelowShading covers the area below a graphY1 =
8 Example 1 Calculator Graph This is what the graph of the inequality looks like on a graphing calculator. Notice that we won’t be able to graph the dotted boundary line.
9 Example 2Example 2: Graph the inequality 3x – 5y ≥ 15.yx
10 Example 3Example 3: Graph the inequality 2x > 8yx
13 Solving Systems of Inequalities We now consider systems of linear inequalities such asTo solve such systems graphically means to graph all ordered pairs (x, y) that simultaneously satisfy all the inequalities in the system.The graph is called the solution region for the system (or feasible region.)
14 Solving Systems of Inequalities To find the solution region, we graph each inequality in the system and then take the intersection (overlap) of all the graphs.To find the intersection, lightly shade the solution region for each inequality separately.Darken in the region where the all of the regions overlap. Erase any shading that is not in the overlapping region.Make sure it is very clear which region is the solution of the system (your final answer).
16 Corner PointsA corner point (or vertex) of a solution region is a point in the solution region that is the intersection of two boundary lines.In the previous example, the solution region had a corner point of (4,0) because that was the intersection of the lines y = -1/2 x + 2 and y = x – 4.Corner point
17 Bounded vs. UnboundedA solution region of a system of linear inequalities is BOUNDED if it can be enclosed within a circle.
18 Bounded vs. UnboundedIf it cannot be enclosed within a circle, it is UNBOUNDED.
19 Example 6 Example 6: Solve the system: y x Is the solution bounded or unbounded?
20 Example 6 (on the calculator) Now, Solve the system using the calculator:x
22 Example 7 (continued)xyIs the solution bounded or unbounded?
23 Example 8Example 8: Solve the system and give the coordinates of any corner points (vertices) formed.
24 Example 8 (continued)xyIs the solution bounded or unbounded?
25 ApplicationLabor costs for a farmer are $55 per acre for corn and $45 per acre for soybeans. The farmer wants to spend no more than $6,900 on labor. Let x represent the number of acres of corn and y represent the number of acres of soybeans. Write a system of inequalities to represent the appropriate constraints on x and y. Graphically find the set of feasible solutions (i.e. graph the feasible region.)