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October 16, 2004

三等分の折り方

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中学生に、「頭の体操」をさせようと、長方形の紙を渡しました。
〜〜〜〜〜〜〜
「はい。今あげた紙を三等分してごらん」
「ええー、面積ですか?」「こんな感じですか?」
「ものさし使っていいんですか?」
私が問題を出した途端、口々に自分のことしかいわないで、質問してくるのは、小学生と同じ。
「ちょっと、だまれーーー」
だれも黙らない。小学生と同じ。
仕方がないので、私が黙りました。
しばらくして、やっと子どもの方も気がついてシーーーン。
やっと私の出番。
「あのね、、よく聞きなさいよ。その紙を三等分するの。ただし、相似を使って考えるのよ。」
「ええーーぞうきんはどこにあるんですか?」
とボケをかますやつが必ずいる。
「相似というのはね。、、、」
と相似の説明をまずして、(中学二年生はまだ習っていない)
「さ、、考えてご覧」
しばらく、黙々とやります。
(ああーあれじゃだめだな)と思いながら、しめしめと笑っている意地悪な私。
「先生、これですか?」
と一人の男子がやってくる。
「みんなに見せたらいけないので、」
と言って小さな声で「こうやって、、、次にこうして、、、」と言いながら私に折り方を見せてくれます。
「それじゃ相似を使っていないね。その折り方なら内緒にしなくても大丈夫。間違っているから」
「ガクッ」
とかしているうちに、ついにギブアップして、「はりせん」を折り出す不埒なやつ。折るふりしながら紙飛行機を作り出そうとするやつ。
小学生と同じ。まあ、ここまでかな。そろそろ正解を出そうか。
「じゃね、正解を言うからね、、、」
といって、相似を使った三等分の折り方を教えました。
「こっちの辺が1でそっちが2の相似な△ができるから、」と。
反応はいまひとつ鈍く(習っていないからだろうが)感動を得る事はできませんでしたが、それでも三等分するために、自分たちで工夫していたことは楽しかったようです。相似という言葉がファミリアになったと思います。
「じゃ、、五等分はどうするのか、、、」
と小さな声でいっている子がいました。そうなんですね。次に、さらにと考えていく。いいことです。
「よしよし、その調子でがんばれーーー」
〜〜〜〜〜〜〜〜〜
記憶の定着の第一歩。
「生活に結びつけること」
「経験をさせること」
それが、一番だと思います。
たとえ数学であっても、子どもたちにとっては身近に感じられる物からの導入が大切だと思いました。

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Comments

こんにちは。
以前お邪魔したanti-tobaccoです。数学用のブログを作りましたので、名前を変えました。

実は昨年中1の数学を教えていて、図形に入ったとき、折り紙を授業に何度か取り入れました。何回目かに折り紙を取り入れたとき、一緒にTTをやっていたベテランの先生(私はその前はサブ専門で昨年が初めてメインをやらせていただいて、サブにベテランの先生がついてくださいました)に、折り紙は数学ではない、折り紙の能力と数学とはまったく関係ないと不機嫌そうに言われてしまい、ショックだったことを思い出しました。最近は教科書でも折り紙が取り上げられたり、指導書でも折り紙を使っての指導案があるくらいなのですが…。

子供たちはけっこう楽しそうにやっていたのですが、楽しく数学をしていると遊んでいるとか、逆に折り紙が苦手で数学が嫌いになってしまうことを心配しているのかも、とも思ったりはしましたが、複雑でした。

ところでこの三等分は知りませんでした。三角形を三つ作るのですか?

Posted by: mathedu | October 17, 2004 at 01:04 PM

mathedu さん。
コメント有り難うございます。
そうだったんですか、、、
それはショックでしたね。
私は、折り紙は大切な教材だと思うし、数学を教える上で、必要だと思います。
空間把握にも役に立つし、分数も教えることができるし、優れた教材ではと考えています。
なにより子どもにとって具体的に考えられることがいいですよね、、、
まぁ、いろんな考え方があるんでしょうが。
ところで、三等分の方法、別にエントリーしましたので、ご覧くださいね。
また、いろんなこと教えてください。
では。

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