- 数学の楽園
- 中１
- 正負の数
- D 乗法（掛け算）
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例題 １
次の計算をしなさい。
\( (1) \) \( (+3)\times(+5) \)
\( (2) \) \( (+3)\times(-5) \)
解答
\( (1) \) \( +15 \)
\( (2) \) \( -15 \)
解説
\( (1) \) 矢印の長さを５倍
\begin{xy}
{(0,0) \ar @{-}(48,0)},
{(6,3) \ar @{-}(6,-3)},
{(12,3) \ar @{-}(12,-3)},
{(18,3) \ar @{-}(18,-3)},
{(24,3) \ar @{-}(24,-3)},
{(30,3) \ar @{-}(30,-3)},
{(36,3) \ar @{-}(36,-3)},
{(42,3) \ar @{-}(42,-3)},
(12,-7) *{0}="C",
(18,-7) *{+3}="G",
(42,-7)*{+15}="K",
{(12,5) \ar @{->}(18,5)^{+3}},
{(12,14) \ar @{->}(42,14)^{(+3)\times(+5)}},
\end{xy}
\( (2) \) 矢印の長さを反対に５倍
\begin{xy}
{(0,0) \ar @{-}(48,0)},
{(6,3) \ar @{-}(6,-3)},
{(12,3) \ar @{-}(12,-3)},
{(18,3) \ar @{-}(18,-3)},
{(24,3) \ar @{-}(24,-3)},
{(30,3) \ar @{-}(30,-3)},
{(36,3) \ar @{-}(36,-3)},
{(42,3) \ar @{-}(42,-3)},
(36,-7) *{0}="C",
(42,-7) *{+3}="G",
(6,-7)*{-15}="K",
{(36,5) \ar @{->}(42,5)^{+3}},
{(36,14) \ar @{->}(6,14)_{(+3)\times(-5)}},
\end{xy}
例題 ２
次の計算をしなさい。
\( (1) \) \( (-3)\times(+5) \)
\( (2) \) \( (-3)\times(-5) \)
解答
\( (1) \) \( -15 \)
\( (2) \) \( +15 \)
解説
\( (1) \) 矢印の長さを５倍
\begin{xy}
{(0,0) \ar @{-}(48,0)},
{(6,3) \ar @{-}(6,-3)},
{(12,3) \ar @{-}(12,-3)},
{(18,3) \ar @{-}(18,-3)},
{(24,3) \ar @{-}(24,-3)},
{(30,3) \ar @{-}(30,-3)},
{(36,3) \ar @{-}(36,-3)},
{(42,3) \ar @{-}(42,-3)},
(36,-7) *{0}="C",
(30,-7) *{-3}="G",
{(36,5) \ar @{->}(30,5)_{-3}},
{(36,14) \ar @{->}(6,14)_{(-3)\times(+5)}},
\end{xy}
\( (2) \) 矢印の長さを反対に５倍
\begin{xy}
{(0,0) \ar @{-}(48,0)},
{(6,3) \ar @{-}(6,-3)},
{(12,3) \ar @{-}(12,-3)},
{(18,3) \ar @{-}(18,-3)},
{(24,3) \ar @{-}(24,-3)},
{(30,3) \ar @{-}(30,-3)},
{(36,3) \ar @{-}(36,-3)},
{(42,3) \ar @{-}(42,-3)},
(12,-7) *{0}="C",
(6,-7) *{-3}="G",
{(12,5) \ar @{->}(6,5)_{-3}},
{(12,14) \ar @{->}(42,14)^{(-3)\times(-5)}},
\end{xy}
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