に分け，後者のそれぞれについては，「補助線の追加」のときの要領で，構成的に作図を
していく。
例えば，外心の図の場合， 元にする点： ３点（Ａ，Ｂ，Ｃ） と考えるし， ＋−−−−−−−−−−−−−−−−＋ ＋−−−−−−−−−−−−−−−−＋ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ → ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ＋−−−−−−−−−−−−−−−−＋ ＋−−−−−−−−−−−−−−−−＋ 図−2.1 元にする３点 図−2.2 外心の図 四角形の各中点を結んで四角形を作る問題の図の場合， 元にする点： ４点（Ａ，Ｂ，Ｃ，Ｄ） と考える。 ＋−−−−−−−−−−−−−−−−＋ ＋−−−−−−−−−−−−−−−−＋ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ → ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ＋−−−−−−−−−−−−−−−−＋ ＋−−−−−−−−−−−−−−−−＋ 図−2.3 元にする４点 図−2.4 ４角中点このように，図形を
に分け，まず，元にする点を入力し，あとは順次構成するという手順を経るため，作図に
当たって，まず次のことを考える必要がある。
(1) いくつの点を元にするのか。 (2) その後, どういう手順で作図を進めていけばよいのか。このことを，外心の図の作図の場合を例にとって，Geometric Constructor での実際の 手順を追ってみよう。
＋−−−−−−−−−−−−−−−−＋ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ＋−−−−−−−−−−−−−−−−＋ 図−2.5 完成予定図まず，元にする点は３つと考え，またその後の手続きを分析しておく。
＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
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＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
図−2.6 「新しく作図」を選択 図−2.7 「はい」を選択
＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
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＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
図−2.8 元にする点を入力 図−2.9 追加する必要がなくなったら Esc
なお，このとき，必要に応じて，次のような機能が使える。
(1) 座標軸の表示 （Ａを押せば，座標軸の表示／消去）
＋−−−−−−−−−−−−−−−−＋ ＋−−−−−−−−−−−−−−−−＋
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｜ ｜ → ｜ ｜
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＋−−−−−−−−−−−−−−−−＋ ＋−−−−−−−−−−−−−−−−＋
図−2.10 図−2.11
(2) 座標の表示 （Ｃを押せば，座標軸の表示／消去）
＋−−−−−−−−−−−−−−−−＋ ＋−−−−−−−−−−−−−−−−＋
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｜ ｜ → ｜ ｜
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｜ ｜ ｜ ｜
｜ ｜ ｜ ｜
＋−−−−−−−−−−−−−−−−＋ ＋−−−−−−−−−−−−−−−−＋
図−2.12 図−2.13
(3) Ｈを押せば，原点に移動
＋−−−−−−−−−−−−−−−−＋ ＋−−−−−−−−−−−−−−−−＋
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｜ ｜ ｜ ｜
｜ ｜ → ｜ ｜
｜ ｜ ｜ ｜
｜ ｜ ｜ ｜
｜ ｜ ｜ ｜
＋−−−−−−−−−−−−−−−−＋ ＋−−−−−−−−−−−−−−−−＋
図−2.14 図−2.15
(4) 速度の切り換え
・Ｓ：１ドットずつ
・Ｍ：５ドットずつ
・Ｆ：10ドットずつ
・１〜５：その長さ分（ドットではない）
・Ｏ：オプション（ドット数で，自由に設定可能）
次に三角形を作図するため，「線分，多角形」を選択し，「多角形」を選択。そして，
「３」あるいは「０」を入力。↓↑を使って３点を指定すれば，三角形が作図される。
＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
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＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
図−2.16「線分，多角形」を選択 図−2.17 「多角形」を選択
＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
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＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
図−2.18「３」角形を入力（０でも可） 図−2.19↑↓を使って３点を指定
＋−−−−−−−−−−−−−−−−−−＋
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＋−−−−−−−−−−−−−−−−−−＋
図−2.20三角形の作図終了
次に垂直二等分線を作図したい。これは直線なので，次のような流れの入力になる。
＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
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＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
図−2.21 「直線」を選択 図−2.22 「垂直二等分線」を選択
＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
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＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
図−2.23 ↑↓を使って線分を指定 図−2.24 垂直二等分線の作図終了
これを３回繰り返すと，完成予定図が得られる。なお，外心そのものが必要ならば，更
に，交点を「点」として意識化しなければならないので，「点」の中の「様々な交点」の
中の「２直線の交点」を指定し，作図する必要がある。
＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
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＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
図−2.25 「点」を選択 図−2.26 「２直線の交点」を選択
＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
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＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋
図−2.27 ２つの直線を選択 図−2.28 出来上がり
＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ 図−2.29 「編集」を選択 図−2.30 「データ表示」を選択「データ表示」の結果は，ファイルとして出力したものを，簡易エディタで表示してい る。印刷したければ，簡易エディタ内からも印刷できるし，DOS 上で，PRINT コマンドを 使ってもいい。
＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ 図−2.31「作図データ」の内容 図−2.32 「幾何対象」の内容
(1) (2) ＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ 図−2.33 平行四辺形 図−2.34 垂足三角形 (3) (4) ＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ 図−2.35 辺の中点を結んで三角形 図−2.36 辺を2:1 に内分して三角形 (5) (6) ＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ 図−2.37 (4) の手続きを２回繰り返す 図−2.38 角の２等分から内心 (7) (8) ＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ｜ ＋−−−−−−−−−−−−−−−−−−＋−−−−−−−−−−−−−−−−−−−＋ 図−2.39 角の３等分線 図−2.40 モーレーの定理