使用 FOIL 法展開 $$$\left(8 y - 1\right) \left(y - 3\right)$$$

使用 FOIL 法將 $$$\left(8 y - 1\right) \left(y - 3\right)$$$ 相乘。

$$$\left({\color{red}\left(8 y\right)} + {\color{purple}\left(-1\right)}\right) \left({\color{green}\left(y\right)} + {\color{blue}\left(-3\right)}\right) = \underbrace{{\color{red}\left(8 y\right)} {\color{green}\left(y\right)}}_{\text{第一}} + \underbrace{{\color{red}\left(8 y\right)} {\color{blue}\left(-3\right)}}_{\text{外部}} + \underbrace{{\color{purple}\left(-1\right)} {\color{green}\left(y\right)}}_{\text{內部}} + \underbrace{{\color{purple}\left(-1\right)} {\color{blue}\left(-3\right)}}_{\text{末頁}} = 8 y^{2} - 24 y - y + 3 = 8 y^{2} - 25 y + 3$$$

$$$\left(8 y - 1\right) \left(y - 3\right) = 8 y^{2} - 25 y + 3$$$A