lessons/课程/插图/01-欧拉路径/00-欧拉-02-度数配对.svg

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  <title id="title">欧拉路径中间点的度数配对</title>
  <desc id="desc">四条边在中间点 X 成两组进入离开配对，起终点可各剩一条。</desc>
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  <text x="32" y="35" class="note">路线内部的 X：每次进来，都要从另一条边离开。</text>
  <line class="line" x1="135" y1="220" x2="370" y2="140"/><line class="line" x1="135" y1="65" x2="370" y2="140"/><line class="line" x1="605" y1="65" x2="370" y2="140"/><line class="line" x1="605" y1="220" x2="370" y2="140"/>
  <circle class="node" cx="370" cy="140" r="42"/><text class="label" x="360" y="150">X</text>
  <path class="pair" d="M150 64 Q300 28 355 113" fill="none" marker-end="url(#g)"/><path class="pair" d="M385 113 Q455 28 590 64" fill="none" marker-end="url(#g)"/>
  <path d="M150 220 Q300 258 355 167" stroke="#d97706" stroke-width="7" fill="none" marker-end="url(#o)"/><path d="M385 167 Q455 258 590 220" stroke="#d97706" stroke-width="7" fill="none" marker-end="url(#o)"/>
  <text x="47" y="261" class="note">绿色一对、橙色一对：所以中间点度数为偶数。</text>
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