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

$$ \left( \color{blue}{y-3} \right) \cdot \left( \color{orangered}{y+3} \right) = y^2-9 $$

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

$$ \begin{aligned} \left( \color{blue}{ y-3}\right) \cdot \left( \color{orangered}{ y+3}\right) &= \underbrace{ \color{blue}{y} \cdot \color{orangered}{y} }_{\text{FIRST}} + \underbrace{ \color{blue}{y} \cdot \color{orangered}{3} }_{\text{OUTER}} + \underbrace{ \left( \color{blue}{-3} \right) \cdot \color{orangered}{y} }_{\text{INNER}} + \underbrace{ \left( \color{blue}{-3} \right) \cdot \color{orangered}{3} }_{\text{LAST}} = \\ &= y^2 + 3y + \left( -3y\right) + \left( -9\right) = \\ &= y^2 + 3y + \left( -3y\right) + \left( -9\right) = \\ &= y^2-9; \end{aligned} $$

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