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# 善用評估資料提升學與教效能 學校經驗分享（一） ： 有向數的運算 - PowerPoint PPT Presentation

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### 善用評估資料提升學與教效能學校經驗分享（一） ：有向數的運算

“負負得正”

1. TSA 數據–有向數的運算

NA1-3作有向數加、減、乘、除運算(每一數式中作不超過3次運算)

2006MC1 Q.1, MC4 Q.1

8.4% 11.6% 69.3% 10.3%

2007MC1 Q.1

80.2% 6.9% 10.7% 1.7%

1. TSA 數據–有向數的運算

NA1-3作有向數加、減、乘、除運算(每一數式中作不超過3次運算)

2008MC1 Q.1, MC2 Q.1

6%

8%

9%

76%

• 先不引入括號，單從連續加減式入手

• 從「減數多於加數」處引入負數

• 削弱「負負得正」口訣錯誤用於加減數的傾向

• 先處理正數乘負數及加乘混合式

• 待教了負數乘負數後才處理負數的減法

• 將算式中的所有乘數連負號間線，訓練學生先乘除後加減，及減少負號運算錯誤

• 以觀察規律的形式引入「負負得正」，不提其他的情景，以免引起混亂

• 將減負數看成 –1乘以該負數， 例如： –(–2) = –1(–2) = 2再讓學生練習折括號。

• 神奇方陣、乘法鐵三角、加括號練習輔助教學

• 目的是先讓學生體會運算過程，不拘泥於算式表達

• 提供經驗基礎

e.g. (–6) + (–3) – (–2)

e.g.

e.g. –9 – 2(–5) = –9 + 10 = ...

e.g. –9 – 2(–5) = ...