<div style="padding:40px;color:#cbccc6"><h1>二重积分（黎曼柱）</h1><p>矩形区域上 f=x²+y² 的二重积分数值估计。</p><div style="padding:20px;background:#0d1017;border-left:3px solid #ffb454"><span class="katex-display"><span class="katex"><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:2.2717em;vertical-align:-0.9117em;"></span><span class="mop"><span class="mop op-symbol large-op" style="margin-right:0.4445em;position:relative;top:-0.001em;">∬</span><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist" style="height:-0.4334em;"><span style="top:-1.7883em;margin-left:-0.4445em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mathnormal mtight" style="margin-right:0.0077em;">R</span></span></span></span><span class="vlist-s"></span></span><span class="vlist-r"><span class="vlist" style="height:0.9117em;"><span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal" style="margin-right:0.1076em;">f</span><span class="mopen">(</span><span class="mord mathnormal">x</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal" style="margin-right:0.0359em;">y</span><span class="mclose">)</span><span class="mord mathnormal">d</span><span class="mord mathnormal">A</span></span></span></span></span></div><p style="color:#707a8c">该页面需要 JavaScript 进行交互式可视化。</p></div>