FOIL 計算器

使用 FOIL 法將 $$$\left(2 x + 1\right) \left(5 x + 7\right)$$$ 相乘。

$$$\left({\color{red}\left(2 x\right)} + {\color{purple}\left(1\right)}\right) \left({\color{green}\left(5 x\right)} + {\color{blue}\left(7\right)}\right) = \underbrace{{\color{red}\left(2 x\right)} {\color{green}\left(5 x\right)}}_{\text{第一}} + \underbrace{{\color{red}\left(2 x\right)} {\color{blue}\left(7\right)}}_{\text{外部}} + \underbrace{{\color{purple}\left(1\right)} {\color{green}\left(5 x\right)}}_{\text{內部}} + \underbrace{{\color{purple}\left(1\right)} {\color{blue}\left(7\right)}}_{\text{末頁}} = 10 x^{2} + 14 x + 5 x + 7 = 10 x^{2} + 19 x + 7$$$

$$$\left(2 x + 1\right) \left(5 x + 7\right) = 10 x^{2} + 19 x + 7$$$A