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<body>
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    <!-- SIDEBAR -->
    <aside aria-label="Course overview">
      <div class="logo" role="banner">
        <div class="mark">∫d</div>
        <div>
          <h1>Calculus Portfolio</h1>
          <p>Introduction to Calculus — Differential & Integral</p>
        </div>
      </div>

      <div class="sparkle" aria-hidden="true"></div>

      <div class="meta" aria-hidden="true">
        <div class="chip">Level: Introductory</div>
        <div class="chip">Duration: 10–12 weeks</div>
        <div class="chip">Format: Theory + Demo</div>
      </div>

      <p class="summary">
        Calculus studies continuous change. This portfolio summarizes the course objectives, outline, key concepts (limits, derivatives, integrals), and includes a tiny interactive demo illustrating how a secant slope approaches a derivative (tangent slope).
      </p>

      <div class="objectives" aria-labelledby="obj">
        <h3 id="obj">Course Objectives</h3>
        <ul>
          <li>Understand limits, derivatives & integrals</li>
          <li>Apply techniques to physics, engineering & economics</li>
          <li>Analyze & model real-world functions</li>
          <li>Use derivatives to find maxima/minima</li>
        </ul>
      </div>

      <div style="margin-top:14px">
        <button class="cta" id="downloadBtn" title="Save as PDF (print)">
          📄 Save / Print
        </button>
      </div>

      <div style="margin-top:18px">
        <small style="color:var(--muted)">Author: Calculus Instructor • Prepared as a student portfolio</small>
      </div>
    </aside>

    <!-- MAIN -->
    <main>
      <header class="port">
        <div class="title">
          <div>
            <h2>Introduction to Calculus</h2>
            <p>Understanding differential & integral calculus — core ideas, examples, and applications.</p>
          </div>
        </div>

        <div class="badge">Essentials</div>
      </header>

      <!-- Course Outline -->
      <section class="block" aria-labelledby="outlineTitle">
        <h3 id="outlineTitle">Course Outline</h3>
        <div class="outline-grid" role="list">
          <div class="outline-item" role="listitem">
            <strong>Differential Calculus</strong>
            Limits • Derivatives • Applications (tangent lines, rates, optimization)
          </div>
          <div class="outline-item" role="listitem">
            <strong>Integral Calculus</strong>
            Indefinite/Definite Integrals • Techniques • Area & accumulation problems
          </div>
          <div class="outline-item" role="listitem">
            <strong>Foundations</strong>
            Limits, continuity, algebra of functions
          </div>
          <div class="outline-item" role="listitem">
            <strong>Applications</strong>
            Physics (velocity/acceleration), engineering, economics & area computations
          </div>
        </div>
      </section>

      <!-- Definitions and Concepts -->
      <section class="block" aria-labelledby="defs">
        <h3 id="defs">What is Calculus?</h3>
        <p>
          Calculus is the study of continuous change. Historically developed by Newton and Leibniz, it focuses on two complementary ideas:
        </p>

        <div class="accordion" id="accordion">
          <div class="acco-item">
            <button class="acco-head" data-target="a1"><h4>Differential Calculus</h4><span></span></button>
            <div class="acco-body" id="a1">
              Differential calculus studies rates of change (derivatives). The derivative f'(x) = dy/dx measures how the function y = f(x) changes as x changes. It arises from the limit of a quotient: the slope of the secant line approaches the slope of the tangent line.
            </div>
          </div>

          <div class="acco-item">
            <button class="acco-head" data-target="a2"><h4>Integral Calculus</h4><span></span></button>
            <div class="acco-body" id="a2">
              Integral calculus reverses differentiation: integration accumulates small pieces to get a whole. Indefinite integrals include an arbitrary constant (C); definite integrals compute accumulated values like area under a curve.
            </div>
          </div>

          <div class="acco-item">
            <button class="acco-head" data-target="a3"><h4>Limits & Continuity</h4><span></span></button>
            <div class="acco-body" id="a3">
              Limits describe the behavior of a function as the input approaches a certain value. Continuity means the limit equals the function value. Limits are the foundation on which both derivatives and integrals are built.
            </div>
          </div>
        </div>
      </section>

      <!-- Interactive mini-demo -->
      <section class="block" aria-labelledby="demoTitle">
        <h3 id="demoTitle">Interactive Demo — Secant → Tangent (Derivative)</h3>
        <p style="margin-bottom:12px;color:var(--muted)">Use the slider to move the second point (h). The slope of the secant line approaches the tangent slope as h → 0 for f(x) = x² at x = 1.</p>

        <div class="demo" role="application" aria-label="Derivative demo">
          <div class="graph" id="svgWrap" aria-hidden="false">
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            <label for="hRange">h (distance between points): <span id="hVal">0.8</span></label>
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            <div class="val" style="margin-top:12px">
              Secant slope: <strong id="secSlope">2.6</strong>
            </div>
            <div class="val" style="margin-top:6px">
              Tangent (derivative) at x: <strong id="tanSlope">2</strong>
            </div>

            <div style="height:10px"></div>

            <div class="legend" style="margin-top:10px">
              <div class="dot sec" aria-hidden="true"></div><span>Secant</span>
              <div style="width:8px"></div>
              <div class="dot tan" aria-hidden="true"></div><span>Tangent</span>
            </div>
          </div>
        </div>

        <footer class="note">
          <span>Formula shown uses f(x)=x². Derivative f'(x)=2x (so at x=1, tangent slope = 2).</span>
          <span style="opacity:0.9">Try h → 0 to see secant slope approach 2.</span>
        </footer>
      </section>

      <!-- More content -->
      <section class="block" aria-labelledby="addTitle">
        <h3 id="addTitle">Key Formulas & Notes</h3>
        <p style="margin-bottom:8px;color:var(--muted)">
          <strong>Derivative:</strong> f'(x) = limₕ→0 (f(x+h) - f(x))/h<br>
          <strong>Indefinite Integral:</strong> ∫ f(x) dx = F(x) + C<br>
          <strong>Definite Integral:</strong> ∫ₐᵇ f(x) dx = F(b) - F(a)
        </p>

        <div style="display:flex;gap:12px;flex-wrap:wrap;margin-top:8px">
          <div class="chip">Applications: Motion, Area, Optimization</div>
          <div class="chip">Tools: Analytical techniques, substitution, parts</div>
          <div class="chip">Prereqs: Functions, algebra, exponents</div>
        </div>
      </section>

      <!-- Closing -->
      <section style="display:flex;justify-content:space-between;align-items:center;margin-top:8px">
        <small style="color:var(--muted)">Prepared as a student portfolio • Clean, shareable, printable</small>
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      const mapX = x => ( (x - xMin) / (xMax - xMin) ) * (w-60) + 40;
      const mapY = y => h - ( (y - yMin) / (yMax - yMin) ) * (h-40) - 20;

      // draw axes + grid
      function drawAxes(){
        svg.innerHTML = '';
        const ns = 'http://www.w3.org/2000/svg';

        // grid lines
        for(let gx = Math.ceil(xMin); gx<=Math.floor(xMax); gx++){
          const xPos = mapX(gx);
          const line = document.createElementNS(ns,'line');
          line.setAttribute('x1',xPos); line.setAttribute('x2',xPos);
          line.setAttribute('y1',20); line.setAttribute('y2',h-20);
          line.setAttribute('stroke','rgba(255,255,255,0.02)');
          line.setAttribute('stroke-width','1');
          svg.appendChild(line);

          const txt = document.createElementNS(ns,'text');
          txt.setAttribute('x', xPos);
          txt.setAttribute('y', h-6);
          txt.setAttribute('fill','rgba(230,238,248,0.45)');
          txt.setAttribute('font-size','10');
          txt.setAttribute('text-anchor','middle');
          txt.textContent = gx;
          svg.appendChild(txt);
        }

        for(let gy = 0; gy<=8; gy+=1){
          const yPos = mapY(gy);
          const line = document.createElementNS(ns,'line');
          line.setAttribute('y1',yPos); line.setAttribute('y2',yPos);
          line.setAttribute('x1',40); line.setAttribute('x2',w-20);
          line.setAttribute('stroke','rgba(255,255,255,0.02)');
          line.setAttribute('stroke-width','1');
          svg.appendChild(line);
        }

        // axes
        const axisX = document.createElementNS(ns,'line');
        axisX.setAttribute('x1',mapX(xMin)); axisX.setAttribute('x2',mapX(xMax));
        axisX.setAttribute('y1', mapY(0)); axisX.setAttribute('y2', mapY(0));
        axisX.setAttribute('stroke','rgba(230,238,248,0.12)');
        axisX.setAttribute('stroke-width','1.5');
        svg.appendChild(axisX);

        const axisY = document.createElementNS(ns,'line');
        axisY.setAttribute('x1',mapX(0)); axisY.setAttribute('x2',mapX(0));
        axisY.setAttribute('y1', mapY(yMin)); axisY.setAttribute('y2', mapY(yMax));
        axisY.setAttribute('stroke','rgba(230,238,248,0.12)');
        axisY.setAttribute('stroke-width','1.5');
        svg.appendChild(axisY);
      }

      function plotFunction(){
        const ns = 'http://www.w3.org/2000/svg';
        const path = document.createElementNS(ns,'path');
        let d = '';
        const steps = 200;
        for(let i=0;i<=steps;i++){
          const t = i/steps;
          const x = xMin + t*(xMax - xMin);
          const y = x*x; // f(x)=x^2
          const px = mapX(x), py = mapY(y);
          d += (i===0? 'M':'L') + px + ' ' + py + ' ';
        }
        path.setAttribute('d', d);
        path.setAttribute('stroke','rgba(125,211,252,0.95)');
        path.setAttribute('stroke-width','2.2');
        path.setAttribute('fill','none');
        svg.appendChild(path);
      }

      function drawPoints(x, h){
        const ns = 'http://www.w3.org/2000/svg';
        const x1 = x;
        const x2 = x + h;
        const y1 = x1*x1;
        const y2 = x2*x2;

        const p1x = mapX(x1), p1y = mapY(y1);
        const p2x = mapX(x2), p2y = mapY(y2);

        // points
        const c1 = document.createElementNS(ns,'circle');
        c1.setAttribute('cx',p1x); c1.setAttribute('cy',p1y); c1.setAttribute.