6.5 Graphing Linear Inequalities in Two Variables 7.6 Graphing Linear Inequalities System Objectives 1. Graph linear inequalities. 2. Graph systems of linear inequalities. Linear Inequalities A linear inequality in two variables is an inequality that can be written in the form Ax + By < C, where A, B, and C are real numbers and A and B are not both zero. The symbol < may be replaced with , >, or . The solution set of an inequality is the set of all ordered pairs that make it true. The graph of an inequality represents its solution set. To Graph a Linear Inequality Step (1) Solve for y, convert the inequalities to Slope-Intercept Form. If one variable is missing, solve it and go to step (2). (2) Graph the related equation. ** If the inequality symbol is < or >, draw the line dashed. ** If the inequality symbol is or , draw the line solid. (3) If y < or y , shade the region BELOW the line If y > or y , shade the region ABOVE the line If x < or x , shade the region LEFT to the line If x > or x , shade the region RIGHT to the line Example Graph y > x 4. (1) Already in S-I form. (2) The related equation is y = x 4. Use a dashed line because the inequality symbol is >. This indicates that the line itself is not in the solution set. (3) Determine which half-plane satisfies the inequality. y>x4 “>” shade above Example Graph: 4x + 2y 8 1. Convert to S-I form: y -2x + 4 2. Graph the related equation. 3. Determine which halfplane satisfies the inequality. “y ” shade below Example Graph 2x – 4 > 0 . 1. One variable is missing. Solve it: x>2 2. Graph the related equation x=2 3. Determine which halfplane satisfies the inequality. “x >” shade the right. Example Graph 8 - 3y 2 . 1. One variable is missing. Solve it: y2 2. Graph the related equation y=2 3. Determine the region to be shaded. “y ” shaded below 7.6 Systems of Linear Inequalities Graph the solution set of the system. x y3 x y 1 First, we graph x + y 3 using a solid line. y -x+3 “above” Next, we graph x y > 1 using a dashed line. y< x–1 “below” The solution set of the system of equations is the region shaded both red and green, including part of the line x + y = 3. Example Graph the following system of inequalities and find the coordinates of any vertices formed: y20 x y 2 x y0 We graph the related equations using solid lines. We shade the region common to all three solution sets. Example continued y20 (1 ) The system of equations from inequalities (1) and (3): x y 2 (2 ) y+2=0 x y0 (3 ) x+y=0 To find the vertices, we solve The vertex is (2, 2). three systems of equations. The system of equations from inequalities (2) and (3): The system of equations from inequalities (1) and (2): x + y = 2 x+y=0 y+2=0 The vertex is (1, 1). x + y = 2 The vertex is (4, 2). Summary 1. To graph a two-variable linear inequality, graph the related equation first (variable y must be solved) with appropriate boundary line: “<” and “>” use dash line “≤” and “≥” use solid line 2. “y < …” and “y ≤ …” shade the region below 3. “y > …” and “y ≥ …” shade the region above 4. “x < …” and “x ≤ …” shade the region left 5. “x > …” and “x ≥ …” shade the region right 6. When graphing the linear inequality system, follow the step 1 ~ 3 and choose the region shaded most. Assignment 6.5 P 363 #’s 10 - 22 (even), 32 - 40 (even), 45 - 60 (even) 7.6 P 435 #’s 9 - 26