21/08/2025
Learn Inequalities
📚 Inequalities: A Comprehensive Guide 🦮
🔹 In mathematics, equations tell us when two expressions are equal. Inequalities, on the other hand, describe a relationship of greater than, less than, or not equal to. They are powerful tools for comparing values, defining ranges, and analyzing constraints in real-world problems such as optimization, economics, and physics.
✅ Symbols of Inequalities
• a < b ⇒ a is less than b
• a > b ⇒ a is greater than b
• a ≤ b ⇒ a is less than or equal to b
• a ≥ b ⇒ a is greater than or equal to b
• a ≠ b ⇒ a is not equal to b
✅ Rules of Inequalities
Working with inequalities is similar to working with equations, but with one important difference:
• Adding/Subtracting the same number:
If a < b, then a + c < b + c.
• Multiplying/Dividing by a positive number:
If a < b, then ac < bc for c > 0.
• Multiplying/Dividing by a negative number:
The inequality sign reverses.
If a < b, then ac > bc for c < 0.
⚠️ This reversal rule is the most crucial difference between solving equations and inequalities.
✅ Linear Inequalities
Example: Solve 2x - 3 < 7.
Solution:
2x - 3 < 7
⇒2x < 10
⇒x < 5
Solution set: x ∈ (-∞, 5).
✅ Quadratic Inequalities
Quadratic inequalities involve parabolas and require analyzing intervals.
Steps:
1. Rewrite in standard form ax² + bx + c > or < 0.
2. Solve the corresponding quadratic equation ax² + bx + c = 0.
3. Use the sign diagram or parabola sketch to test intervals.
Example: Solve; x² - 5x + 6 > 0.
Factorize:
(x - 2)(x - 3) > 0
Critical points: x = 2, x = 3.
Sign analysis shows parabola opens upward, so inequality holds when x < 2 or x > 3.
Solution set: x ∈ (-∞, 2) ∪ (3, ∞)
✅ Simultaneous Inequalities
We can solve multiple inequalities together, often graphically or through interval comparison.
Example: Solve: x + 2 > 0 and 2x - 5 < 3
From first inequality: x > -2.
From second inequality: 2x < 8 ⇒x < 4.
Combined solution: -2 < x < 4
✅ Graphical Representation
• On a number line, inequalities are represented by shaded intervals.
• On a coordinate plane, inequalities define regions (half-planes, bounded regions).
For instance, y ≥ 2x + 1 represents the half-plane above the line y = 2x + 1.
✅ Applications of Inequalities
• Optimization problems (e.g., linear programming).
• Defining domains of functions (e.g., square roots require non-negativity).
• Bounding values in analysis (estimation, error control).
• Inequalities in mathematics (AM–GM, Cauchy–Schwarz, Hölder’s inequality, etc.).
💡🌟 Inequalities extend the power of equations by not just identifying equal values, but by describing ranges of possible values. From solving simple one-variable inequalities to analyzing quadratic ranges and shading solution regions, inequalities are a bridge between algebra and advanced fields like optimization and analysis.