Question
Answer
$$(3x+1)(3x-1)=9x^2-1$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(3x+1)(3x-1)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}9x^2-3x+3x-1 \xlongequal{ } \\[1 em] & \xlongequal{ }9x^2 -\cancel{3x}+ \cancel{3x}-1 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}9x^2-1\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{3x+1}\right) $ by each term in $ \left( 3x-1\right) $. $$ \left( \color{blue}{3x+1}\right) \cdot \left( 3x-1\right) = 9x^2 -\cancel{3x}+ \cancel{3x}-1 $$ |
| ② | Combine like terms: $$ 9x^2 \, \color{blue}{ -\cancel{3x}} \,+ \, \color{blue}{ \cancel{3x}} \,-1 = 9x^2-1 $$ |
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