Chapter 1: Problem 5
Solve the following inequalities: (a) \(|5 x-2| \leq 4\) (b) \(|1-3 x|>8\) (c) \(|7 x+4| \geq 3\) (d) \(|6-5 x|<7\)
Short Answer
Expert verified
(a) \(-\frac{2}{5} \leq x \leq \frac{6}{5}\), (b) \(x < -\frac{7}{3}\) or \(x > 3\), (c) \(x \geq -\frac{1}{7}\) or \(x \leq -1\), (d) \(-\frac{1}{5} < x < \frac{13}{5}\).
Step by step solution
01
Understanding the Absolute Value Inequality
To solve an inequality involving an absolute value, such as \(|ax+b| \leq c\), understand that this splits into two cases: \(-c \leq ax+b \leq c\). For \(|ax+b|>c\), the cases are \(ax+b>c\) or \(ax+b<-c\). Similarly, \(|ax+b| \geq c\) results in \(ax+b \geq c\) or \(ax+b \leq -c\).
02
Case (a): Solve \(|5x-2| \leq 4\)
First, write the inequality as two separate inequalities: \(-4 \leq 5x-2 \leq 4\). Solve for \(x\): 1. First inequality: \(-4 \leq 5x-2\) Add 2 to both sides: \(-2 \leq 5x\) Divide by 5: \(-\frac{2}{5} \leq x\).2. Second inequality: \(5x-2 \leq 4\) Add 2 to both sides: \(5x \leq 6\) Divide by 5: \(x \leq \frac{6}{5}\).Therefore, the solution is \(-\frac{2}{5} \leq x \leq \frac{6}{5}\).
03
Case (b): Solve \(|1-3x|>8\)
This splits into two inequalities: 1. \(1-3x>8\) Subtract 1 from both sides: \(-3x>7\) Divide by \(-3\) (reverse the inequality): \(x<-\frac{7}{3}\).2. \(1-3x<-8\) Subtract 1 from both sides: \(-3x<-9\) Divide by \(-3\) (reverse the inequality): \(x>3\).So the solution is \(x<-\frac{7}{3}\) or \(x>3\).
04
Case (c): Solve \(|7x+4| \geq 3\)
This results in two inequalities:1. \(7x+4 \geq 3\) Subtract 4 from both sides: \(7x \geq -1\) Divide by 7: \(x \geq -\frac{1}{7}\).2. \(7x+4 \leq -3\) Subtract 4 from both sides: \(7x \leq -7\) Divide by 7: \(x \leq -1\).The solution is \(x \geq -\frac{1}{7}\) or \(x \leq -1\).
05
Case (d): Solve \(|6-5x|
Split it into two inequalities: \(-7 < 6-5x < 7\). Solve as follows:1. First inequality: \(-7 < 6-5x\) Subtract 6 from both sides: \(-13 < -5x\) Divide by \(-5\) (reverse the inequality): \(x < \frac{13}{5}\).2. Second inequality: \(6-5x < 7\) Subtract 6 from both sides: \(-5x < 1\) Divide by \(-5\) (reverse the inequality): \(x > -\frac{1}{5}\).Therefore, the solution for this case is \(-\frac{1}{5} < x < \frac{13}{5}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Solving Inequalities
When solving inequalities, the objective is to find a range of values that satisfy the given inequality. Unlike equations, where you're looking for specific values, here you're finding a set or interval of numbers. Let's take an example: if you have the inequality \( x + 3 > 5 \), you're interested in determining which values of \( x \) make this statement true.
To solve it:
To solve it:
- Subtract 3 from both sides to isolate \( x \).
- This gives you \( x > 2 \), so any number greater than 2 will work.
Case Analysis
Case analysis is a powerful approach for tackling inequalities involving absolute values. Absolute value expresses the distance of a number from zero, so \(|x| = a\) means \(x\) is \(a\) units away from zero, either positively or negatively. Hence, it involves two scenarios.
Consider a typical absolute value inequality like \(|x - 5| \leq 3\). This implies two cases that you need to examine simultaneously:
Consider a typical absolute value inequality like \(|x - 5| \leq 3\). This implies two cases that you need to examine simultaneously:
- Case 1: \( x - 5 \leq 3 \)
- Case 2: \( x - 5 \geq -3 \)
Reverse Inequality
Reversing inequalities occurs when you multiply or divide both sides of an inequality by a negative number. This is a critical rule to remember because it works differently than when dealing with equations.
For example, if you have \(-3x > 6\), and you decide to divide both sides by \(-3\) to solve for \(x\), the inequality sign flips. So, \(x < -2\).
Here's a step-by-step process for reversing inequalities:
For example, if you have \(-3x > 6\), and you decide to divide both sides by \(-3\) to solve for \(x\), the inequality sign flips. So, \(x < -2\).
Here's a step-by-step process for reversing inequalities:
- Identify when multiplying or dividing by a negative number is necessary.
- After the operation, flip the inequality sign to maintain a true statement.
- Continue solving like normal equations from there.
Splitting Absolute Value Inequalities
Splitting absolute value inequalities involves rewriting them into a form that can be solved using regular inequality techniques. Absolute value inequalities, such as \( |ax+b| < c \), imply a range without explicitly showing it at first glance.
These are split into logical parts:
These are split into logical parts:
- If \( |ax+b| \leq c \), consider \(-c \leq ax+b \leq c\).
- If \( |ax+b| > c \), use separate conditions: \( ax+b > c \quad\text{or}\quad ax+b < -c \).