Question
Answer
$$(9x^2-5)(9x^2+5)=81x^4-25$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}(9x^2-5)(9x^2+5)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}81x^4+45x^2-45x^2-25 \xlongequal{ } \\[1 em] & \xlongequal{ }81x^4+ \cancel{45x^2} -\cancel{45x^2}-25 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}81x^4-25\end{aligned} $$ | |
| ① | Multiply each term of $ \left( \color{blue}{9x^2-5}\right) $ by each term in $ \left( 9x^2+5\right) $. $$ \left( \color{blue}{9x^2-5}\right) \cdot \left( 9x^2+5\right) = 81x^4+ \cancel{45x^2} -\cancel{45x^2}-25 $$ |
| ② | Combine like terms: $$ 81x^4+ \, \color{blue}{ \cancel{45x^2}} \, \, \color{blue}{ -\cancel{45x^2}} \,-25 = 81x^4-25 $$ |
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