4.1 Solving Linear Inequalities 11/2/2012

You have learned how to solve equations with 1 variable. Ex. x + 3 = x = 4 Ex. x - 5 = x = 7 Ex. 3x = x = 4 Ex. y = 6 2 y = 12 ·2 2·

To solve inequality in 1 variable All the rules apply for solving equations in 1 variable except when dividing or multiplying both sides by a negative number. Rule: When multiplying or dividing both sides of an inequality by a negative number, reverse the inequality symbol.

Example 1 Inequality with a Variable on One Side Solve the inequality. a.b. > x 4 – 6 –– ≥ 5y 213 – + SOLUTION a. > x 4 – 6 – Write original inequality. > x2 – Add 4 to each side. ANSWER The solution is all real numbers greater than 2. – + 4

Example 1 Inequality with a Variable on One Side b. – ≥ 5y 213 – + Write original inequality. – ≥ 5y5y15 – Subtract 2 from each side. ANSWER The solution is all real numbers less than or equal to 3. Divide each side by 5 and reverse the inequality. – y ≤

Graphing the solution of an inequality in 1 variable. For > or <, doughnut ( ) For ≤ or ≥, solid circle ( ) Then shade the side of the number line according to which way the inequality symbol is pointing when the variable is on the left side Ex. x > -1 Ex. x ≤ 3

Example 2 Inequality with a Variable on Both Sides Solve. Graph the solution. Add 2x to each side. < 7 2x – 1 < 7 4x1 2x –– SOLUTION Write original inequality. < 7 4x1 2x –– < 2x2x – 6 – Subtract 7 from each side. > x3 Divide each side by 2 and reverse the inequality. – +2x -2

Example 2 Inequality with a Variable on Both Sides ANSWER The solution is all real numbers greater than 3. The graph is shown at the bottom – 0

Checkpoint Solve the inequality. Then graph your solution. Solve an Inequality <x ≤ 4 x – 2. ANSWER < x ≥x 1 – 02 2 –

Checkpoint Solve the inequality. Then graph your solution. – x > 2x 3 4. Solve an Inequality 2 > 2x 1 – 3. 3 x > ANSWER x >

Example 3 Use a Simple Inequality Amusement Park Admission to an amusement park costs $9 and each ride ticket costs $1.50. The total amount A in dollars spent is given by where t is the number of ride tickets. Use an inequality to describe the number of ride tickets you can buy if you have at most $45 to spend at the park. = A1.5t + 9 SOLUTION The most money you can spend is $45. A45 ≤ Substitute for A. 45 ≤ 1.5t Subtract 9 from each side. 36 ≤ 1.5t Divide each side by ≤ t ANSWER You can buy up to 24 ride tickets.

COMPOUND INEQUALITY 2 simple inequalities joined by the word “and” or the word “or”. Ex: AND All real numbers greater than or equal to -2 AND less than 1. Ex: OR All real numbers less than -1 OR greater than or equal to 2 -2≤ x < 1 x < -1 or x ≥ 2

Example 4 Solve an “Or” Compound Inequality Solve or 3x3x + 28< 2x2x – > SOLUTION Solve each part separately. FIRST INEQUALITYSECOND INEQUALITY 3x3x + 28<2x2x93 – > Write first inequality. Write second inequality. 3x3x6<2x2x12 > Subtract 2 from each side. Add 9 to each side. x2<x6 > Divide each side by 3. Divide each side by 2.

Checkpoint Solve the inequality. Then graph your solution. Solve Compound Inequalities 5. 4x< + 57< 6. 3x3x ≤ + 81 – 8 ≤ ANSWER x2<1< – 2 – 20 x ≤ 3 – 0 ≤ 4 – 2 – 0..

Checkpoint Solve the inequality. Then graph your solution. Solve Compound Inequalities 7. x or ≤ x6 –≥ 1 – ANSWER x 1 or ≤ x5 ≥ x2x60< –– x 4 or – > ANSWER x 4 or – <x3 – > 0 6 – 4 – 2 –

Homework 4.1 p.175 #14-22 even, 23-28all, 30-38even, 40-44all, 50-56even