# 國中數學/負數

## 四則運算

${\displaystyle (+2)\times (+3)=6}$ ${\displaystyle (+6)\div (+3)=2}$

${\displaystyle (+2)\times (-3)=-6}$ ${\displaystyle (+6)\div (-3)=-2}$

${\displaystyle (+6)-(+3)=6{\color {Orange}-3}=3}$ ${\displaystyle (-2)\times (+3)=-6}$ ${\displaystyle (-6)\div (+3)=-2}$

${\displaystyle (+3)-(-3)=3{\color {Orange}+3}=6}$ ${\displaystyle (-2)\times (-3)=6}$ ${\displaystyle (-6)\div (-3)=2}$

## 計算

0被任何數減掉，所得之差為其相反數

0—11＝—11

0被11減掉，所得到的差 ${\displaystyle 0-11=-11}$ ，與減數11互為相反數。

${\displaystyle 36{\color {Orange}{-11}}=25}$

${\displaystyle 36{\color {Orange}{-111}}=-75}$

## 例題

• 基本1. 36-55
• 基本2. (-17)-(-19)
• 基本3. (-30)×(-16)
• 進階1. (-568)-(346-567)
• 進階2. 12+(-3)×[30-(-6)×(-4)]÷3
• 進階3. (-99) ×(-12)
• 進階4. 5+(-2)×|22+3×(-8)|-69÷(-3)
• 進階5. 366+[(36-111)+(36-11)]× 2.22
 答案 基本1. 36-55 =-19 基本2. (-17)-(-19) = -17+19 =2 基本3. (-30)×(-16) =30×16 =480 進階1. (-568)-(346-567) = -568-346+567 = -568+567-346 = -1-346 =-347 進階2. 12+(-3)×[30-(-6)×(-4)]÷3 =12+(-3)×(30-24)÷3 =12+(-3)×6÷3 =12+(-18)÷3 =12+(-6) =6 進階3. (-99) ×(-12) =[(-100)+1]×(-12) =(-100)×(-12)+1×(-12) =1200-12 =1188 進階4. 5+(-2)×|22+3×(-8)|-69÷(-3) =5+(-2)×|22+(-24)|-69÷(-3) =5+(-2)×2-69÷(-3) =5+(-4)-(-23) =24 進階5. 366+[(36-111)+(36-11)]× 2.22 =366+[-75+25]× 2.22 =366-50× 2.22 =366-111 =255

## 延伸閱讀

(+)符號(-)

－2 負二

36－11=25 三十六減十一等於二十五