Multiply polynomial $ \, \color{blue}{ 4x+5 } \, $ by $ \, \color{orangered}{ 4x-5 }$.

$$ \left( \color{blue}{4x+5} \right) \cdot \left( \color{orangered}{4x-5} \right) = 16x^2-25 $$

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

$$ \begin{aligned} \left( \color{blue}{ 4x+5}\right) \cdot \left( \color{orangered}{ 4x-5}\right) &= \underbrace{ \color{blue}{4x} \cdot \color{orangered}{4x} }_{\text{FIRST}} + \underbrace{ \color{blue}{4x} \cdot \left( \color{orangered}{-5} \right) }_{\text{OUTER}} + \underbrace{ \color{blue}{5} \cdot \color{orangered}{4x} }_{\text{INNER}} + \underbrace{ \color{blue}{5} \cdot \left( \color{orangered}{-5} \right) }_{\text{LAST}} = \\ &= 16x^2 + \left( -20x\right) + 20x + \left( -25\right) = \\ &= 16x^2 + \left( -20x\right) + 20x + \left( -25\right) = \\ &= 16x^2-25; \end{aligned} $$

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