Tap the blue circles to see an explanation.
$$ \begin{aligned}x(x^7+1)(x-1)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}(x^8+x)(x-1) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}x^9-x^8+x^2-x\end{aligned} $$ | |
① | Multiply $ \color{blue}{x} $ by $ \left( x^7+1\right) $ $$ \color{blue}{x} \cdot \left( x^7+1\right) = x^8+x $$ |
② | Multiply each term of $ \left( \color{blue}{x^8+x}\right) $ by each term in $ \left( x-1\right) $. $$ \left( \color{blue}{x^8+x}\right) \cdot \left( x-1\right) = x^9-x^8+x^2-x $$ |