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title = "Linear programming"
description = "Graph linear inequalities, identify feasible regions, and optimise objective functions in two variables."
template = "chapter.html"
weight = 19
[extra]
subject = "math"
chapter_id = "linear-programming"
strand = "Number & Algebra"
+++
<div class="book-prose">
<p>
Linear programming finds the best value (maximum or minimum) of a linear objective under linear
constraints. In high school, we solve two-variable problems graphically.
</p>
<h2 id="core-idea" class="book-prose__heading">Core idea</h2>
<p>
Optimize an objective like
\[
P=ax+by
\]
subject to inequalities such as \(x+y\le 12\), \(x\ge0\), \(y\ge0\).
</p>
<h2 id="modeling" class="book-prose__heading">Modeling from context</h2>
<p>
Typical setup:
</p>
<ol>
<li>Define variables (\(x,y\)).</li>
<li>Write constraints from limits/resources.</li>
<li>Write objective function (profit, cost, time, etc.).</li>
<li>Graph constraints and find feasible region.</li>
</ol>
<h2 id="graphing-constraints" class="book-prose__heading">Graphing constraints</h2>
<p>
For each inequality:
</p>
<ul>
<li>Draw boundary line (use solid line for \(\le,\ge\); dashed for \(<,>\)).</li>
<li>Test a point (often origin) to choose correct side.</li>
<li>Combine all valid half-planes.</li>
</ul>
<p>
Include non-negativity constraints \(x\ge0,y\ge0\) unless problem states otherwise.
</p>
<h2 id="feasible-region" class="book-prose__heading">Feasible region</h2>
<p>
The feasible region is where all constraints hold at once. In school-level cases, it is usually a
polygon (possibly unbounded).
</p>
<h2 id="corner-point-principle" class="book-prose__heading">Corner-point principle</h2>
<p>
If an optimum exists for a bounded feasible region, it occurs at a vertex (corner point).
</p>
<p>
So compute all feasible vertices, then evaluate objective at each.
</p>
<h2 id="worked-example" class="book-prose__heading">Worked example</h2>
<p>
Maximize \(P=3x+2y\) subject to:
</p>
<p class="book-formula">\[
x+y\le 8,\quad x+3y\le 12,\quad x\ge0,\ y\ge0.
\]</p>
<p>
Vertices are \((0,0)\), \((8,0)\), \((0,4)\), and intersection of
\(x+y=8\) with \(x+3y=12\), which is \((6,2)\).
</p>
<p>
Evaluate:
</p>
<ul>
<li>\((0,0)\Rightarrow P=0\)</li>
<li>\((8,0)\Rightarrow P=24\)</li>
<li>\((0,4)\Rightarrow P=8\)</li>
<li>\((6,2)\Rightarrow P=22\)</li>
</ul>
<p>
Maximum is \(24\) at \((8,0)\).
</p>
<h2 id="special-cases" class="book-prose__heading">Special cases</h2>
<ul>
<li><strong>No feasible region:</strong> constraints are inconsistent.</li>
<li><strong>Unbounded region:</strong> objective may have no maximum/minimum.</li>
<li><strong>Multiple optima:</strong> objective line parallel to a feasible edge.</li>
</ul>
<h2 id="exam-strategy" class="book-prose__heading">Exam strategy</h2>
<ul>
<li>Label all boundary lines and intercepts clearly.</li>
<li>Show shading logic for each inequality.</li>
<li>List vertex coordinates before evaluating objective.</li>
<li>Give final answer with units and variable interpretation.</li>
</ul>
</div>
<div class="book-prose">
<h2 id="history" class="book-prose__heading">History</h2>
<p>
Linear programming developed in the 20th century for resource allocation and planning. George
Dantzig's simplex method made large optimization problems practical in economics and operations
research.
</p>
<h2 id="derivation" class="book-prose__heading">Derivation and reasoning</h2>
<h3 id="why-corners" class="book-prose__heading">Why corner points matter</h3>
<p>
Objective lines \(ax+by=c\) are parallel for different \(c\). Sliding this line across a polygonal
feasible region reaches the last contact at a vertex (or an entire edge in tie cases).
</p>
<h2 id="checkpoints" class="book-prose__heading">Checkpoints</h2>
<details class="book-question">
<summary class="book-question__prompt">
Plot \(x+y\le6,\ x\ge0,\ y\ge0\). List feasible vertices.
</summary>
<div class="book-question__solution">
<p><strong>Answer:</strong> Vertices: \((0,0)\), \((6,0)\), \((0,6)\).</p>
</div>
</details>
<details class="book-question">
<summary class="book-question__prompt">
Maximize \(P=2x+y\) on vertices \((0,0)\), \((4,0)\), \((1,3)\), \((0,3)\).
</summary>
<div class="book-question__solution">
<p><strong>Answer:</strong> Values \(0,8,5,3\). Maximum \(8\) at \((4,0)\).</p>
</div>
</details>
<details class="book-question">
<summary class="book-question__prompt">
Minimize \(C=5x+3y\) with feasible vertices \((0,2)\), \((2,1)\), \((3,4)\).
</summary>
<div class="book-question__solution">
<p><strong>Answer:</strong> \(C=6,13,27\). Minimum \(6\) at \((0,2)\).</p>
</div>
</details>
<details class="book-question">
<summary class="book-question__prompt">
In a model, why are \(x\ge0,\ y\ge0\) often included?
</summary>
<div class="book-question__solution">
<p><strong>Answer:</strong> Quantities like items, time, or material cannot be negative.</p>
</div>
</details>
<details class="book-question">
<summary class="book-question__prompt">
How can you detect possible multiple optimal solutions graphically?
</summary>
<div class="book-question__solution">
<p><strong>Answer:</strong> Objective line is parallel to a boundary edge where both edge endpoints give the same optimum value.</p>
</div>
</details>
<h2 id="applications" class="book-prose__heading">Applications</h2>
<ul>
<li><strong>Production planning:</strong> maximize profit under labor and material limits.</li>
<li><strong>Transport/logistics:</strong> minimize cost with capacity constraints.</li>
<li><strong>Scheduling:</strong> optimize time allocation under availability rules.</li>
</ul>
<h2 id="references" class="book-prose__heading">References</h2>
<ul>
<li>Standard high-school extension units on graphical linear programming.</li>
<li>Introductory operations research texts on feasible regions and corner-point optimization.</li>
</ul>
</div>

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<div class="book-prose">
<p>
Linear programming finds the best value (maximum or minimum) of a linear objective under linear
constraints. In high school, we solve two-variable problems graphically.
</p>
<h2 id="core-idea" class="book-prose__heading">Core idea</h2>
<p>
Optimize an objective like
\[
P=ax+by
\]
subject to inequalities such as \(x+y\le 12\), \(x\ge0\), \(y\ge0\).
</p>
<h2 id="modeling" class="book-prose__heading">Modeling from context</h2>
<p>
Typical setup:
</p>
<ol>
<li>Define variables (\(x,y\)).</li>
<li>Write constraints from limits/resources.</li>
<li>Write objective function (profit, cost, time, etc.).</li>
<li>Graph constraints and find feasible region.</li>
</ol>
<h2 id="graphing-constraints" class="book-prose__heading">Graphing constraints</h2>
<p>
For each inequality:
</p>
<ul>
<li>Draw boundary line (use solid line for \(\le,\ge\); dashed for \(<,>\)).</li>
<li>Test a point (often origin) to choose correct side.</li>
<li>Combine all valid half-planes.</li>
</ul>
<p>
Include non-negativity constraints \(x\ge0,y\ge0\) unless problem states otherwise.
</p>
<h2 id="feasible-region" class="book-prose__heading">Feasible region</h2>
<p>
The feasible region is where all constraints hold at once. In school-level cases, it is usually a
polygon (possibly unbounded).
</p>
<h2 id="corner-point-principle" class="book-prose__heading">Corner-point principle</h2>
<p>
If an optimum exists for a bounded feasible region, it occurs at a vertex (corner point).
</p>
<p>
So compute all feasible vertices, then evaluate objective at each.
</p>
<h2 id="worked-example" class="book-prose__heading">Worked example</h2>
<p>
Maximize \(P=3x+2y\) subject to:
</p>
<p class="book-formula">\[
x+y\le 8,\quad x+3y\le 12,\quad x\ge0,\ y\ge0.
\]</p>
<p>
Vertices are \((0,0)\), \((8,0)\), \((0,4)\), and intersection of
\(x+y=8\) with \(x+3y=12\), which is \((6,2)\).
</p>
<p>
Evaluate:
</p>
<ul>
<li>\((0,0)\Rightarrow P=0\)</li>
<li>\((8,0)\Rightarrow P=24\)</li>
<li>\((0,4)\Rightarrow P=8\)</li>
<li>\((6,2)\Rightarrow P=22\)</li>
</ul>
<p>
Maximum is \(24\) at \((8,0)\).
</p>
<h2 id="special-cases" class="book-prose__heading">Special cases</h2>
<ul>
<li><strong>No feasible region:</strong> constraints are inconsistent.</li>
<li><strong>Unbounded region:</strong> objective may have no maximum/minimum.</li>
<li><strong>Multiple optima:</strong> objective line parallel to a feasible edge.</li>
</ul>
<h2 id="exam-strategy" class="book-prose__heading">Exam strategy</h2>
<ul>
<li>Label all boundary lines and intercepts clearly.</li>
<li>Show shading logic for each inequality.</li>
<li>List vertex coordinates before evaluating objective.</li>
<li>Give final answer with units and variable interpretation.</li>
</ul>
</div>

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<div class="book-prose">
<h2 id="history" class="book-prose__heading">History</h2>
<p>
Linear programming developed in the 20th century for resource allocation and planning. George
Dantzig's simplex method made large optimization problems practical in economics and operations
research.
</p>
<h2 id="derivation" class="book-prose__heading">Derivation and reasoning</h2>
<h3 id="why-corners" class="book-prose__heading">Why corner points matter</h3>
<p>
Objective lines \(ax+by=c\) are parallel for different \(c\). Sliding this line across a polygonal
feasible region reaches the last contact at a vertex (or an entire edge in tie cases).
</p>
<h2 id="checkpoints" class="book-prose__heading">Checkpoints</h2>
<details class="book-question">
<summary class="book-question__prompt">
Plot \(x+y\le6,\ x\ge0,\ y\ge0\). List feasible vertices.
</summary>
<div class="book-question__solution">
<p><strong>Answer:</strong> Vertices: \((0,0)\), \((6,0)\), \((0,6)\).</p>
</div>
</details>
<details class="book-question">
<summary class="book-question__prompt">
Maximize \(P=2x+y\) on vertices \((0,0)\), \((4,0)\), \((1,3)\), \((0,3)\).
</summary>
<div class="book-question__solution">
<p><strong>Answer:</strong> Values \(0,8,5,3\). Maximum \(8\) at \((4,0)\).</p>
</div>
</details>
<details class="book-question">
<summary class="book-question__prompt">
Minimize \(C=5x+3y\) with feasible vertices \((0,2)\), \((2,1)\), \((3,4)\).
</summary>
<div class="book-question__solution">
<p><strong>Answer:</strong> \(C=6,13,27\). Minimum \(6\) at \((0,2)\).</p>
</div>
</details>
<details class="book-question">
<summary class="book-question__prompt">
In a model, why are \(x\ge0,\ y\ge0\) often included?
</summary>
<div class="book-question__solution">
<p><strong>Answer:</strong> Quantities like items, time, or material cannot be negative.</p>
</div>
</details>
<details class="book-question">
<summary class="book-question__prompt">
How can you detect possible multiple optimal solutions graphically?
</summary>
<div class="book-question__solution">
<p><strong>Answer:</strong> Objective line is parallel to a boundary edge where both edge endpoints give the same optimum value.</p>
</div>
</details>
<h2 id="applications" class="book-prose__heading">Applications</h2>
<ul>
<li><strong>Production planning:</strong> maximize profit under labor and material limits.</li>
<li><strong>Transport/logistics:</strong> minimize cost with capacity constraints.</li>
<li><strong>Scheduling:</strong> optimize time allocation under availability rules.</li>
</ul>
<h2 id="references" class="book-prose__heading">References</h2>
<ul>
<li>Standard high-school extension units on graphical linear programming.</li>
<li>Introductory operations research texts on feasible regions and corner-point optimization.</li>
</ul>
</div>