Multiply polynomial $ \, \color{blue}{ x+3 } \, $ by $ \, \color{orangered}{ x-4 }$.

$$ \left( \color{blue}{x+3} \right) \cdot \left( \color{orangered}{x-4} \right) = x^2-x-12 $$

In this example we are multiplying two binomials so FOIL method can be used.

$$ \begin{aligned} \left( \color{blue}{ x+3}\right) \cdot \left( \color{orangered}{ x-4}\right) &= \underbrace{ \color{blue}{x} \cdot \color{orangered}{x} }_{\text{FIRST}} + \underbrace{ \color{blue}{x} \cdot \left( \color{orangered}{-4} \right) }_{\text{OUTER}} + \underbrace{ \color{blue}{3} \cdot \color{orangered}{x} }_{\text{INNER}} + \underbrace{ \color{blue}{3} \cdot \left( \color{orangered}{-4} \right) }_{\text{LAST}} = \\ &= x^2 + \left( -4x\right) + 3x + \left( -12\right) = \\ &= x^2 + \left( -4x\right) + 3x + \left( -12\right) = \\ &= x^2-x-12; \end{aligned} $$

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