Chapter 8: Problem 69
Solve each inequality. State the solution set using interval notation when possible. \(z^{2} \geq 4(z+3)\)
Short Answer
Expert verified
The solution set is \((-∞, -2] union [6, ∞)\).
Step by step solution
01
Move All Terms to One Side
Start by subtracting both terms on the right-hand side from the left-hand side to set the inequality to zero: \[z^{2} - 4(z+3) \geq 0\]
02
Factor the Quadratic Expression
Factor the expression. \[z^{2} - 4z - 12 = (z - 6)(z + 2)\]
03
Determine the Intervals
The critical points divide the number line into three intervals. Solve the inequality on each of these intervals: 1. \( (-eq«, -2) \) 2. \( (-2, 6) \) 3. \( (6, eq«) \)
04
Test Each Interval
Choose a test point in each interval and plug it into the inequality to determine if it satisfies the inequality: 1. For \(z = -3\) in \((- eq«, -2) \): \[(-3 - 6)(-3 + 2) > 0 \implies -9 > 0\] 2. For \(z = 0\) in \((-2, 6)\): \[(0 - 6)(0 + 2) < 0 \implies -12 < 0\] 3. For \(z = 7\) in \((6, eq«)\): \[ (7 - 6)(7 + 2) > 0 \implies 9 > 0\]
05
Include Boundaries
Consider the critical points, as they are included in the solution set due to the non-strict inequality (\(\geq\)): \(z = 6\) and \(z = -2\)
06
Write Solution in Interval Notation
Combine all intervals that satisfy the inequality: The solution set in interval notation is: \[(-∞, -2] union [6, ∞)\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Quadratic Inequalities
Quadratic inequalities involve expressions where a quadratic polynomial is compared with a value (like zero). A quadratic polynomial has the general form:
- ax² + bx + c
- ax² + bx + c ≥ 0
- ax² + bx + c ≤ 0
- Rearrange the terms to set the inequality to zero.
- Factor the quadratic expression where possible.
- Determine the intervals by solving the equality ax² + bx + c = 0.
- Test points in each interval to determine where the inequality holds true.
Interval Notation
Interval notation helps us express a range of values compactly. We use round brackets
Notation (∞) or (-∞) indicates all values greater than or less than a certain point. For instance, (-∞, 5) represents all numbers less than 5. To express a union of two intervals, use the union symbol
- ( and )
- [ and ]
Notation (∞) or (-∞) indicates all values greater than or less than a certain point. For instance, (-∞, 5) represents all numbers less than 5. To express a union of two intervals, use the union symbol
- (∪)
Factoring
Factoring helps break down complex quadratic expressions into simpler, solvable forms. For example, factoring
- z² - 4(z + 3)
- z² - 4z - 12 = 0
- (z - 6)(z + 2)