Tap the blue circles to see an explanation.
| $$ \begin{aligned}\frac{1}{30}(2k^3+9k^2+13k+9)(3k^2+9k+5)& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{2k^3+9k^2+13k+9}{30}(3k^2+9k+5) \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}\frac{6k^5+45k^4+130k^3+189k^2+146k+45}{30}\end{aligned} $$ | |
| ① | Multiply $ \dfrac{1}{30} $ by $ 2k^3+9k^2+13k+9 $ to get $ \dfrac{ 2k^3+9k^2+13k+9 }{ 30 } $. Step 1: Write $ 2k^3+9k^2+13k+9 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator. Step 2: Multiply numerators and denominators. Step 3: Simplify numerator and denominator. $$ \begin{aligned} \frac{1}{30} \cdot 2k^3+9k^2+13k+9 & \xlongequal{\text{Step 1}} \frac{1}{30} \cdot \frac{2k^3+9k^2+13k+9}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ 1 \cdot \left( 2k^3+9k^2+13k+9 \right) }{ 30 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ 2k^3+9k^2+13k+9 }{ 30 } \end{aligned} $$ |
| ② | Multiply $ \dfrac{2k^3+9k^2+13k+9}{30} $ by $ 3k^2+9k+5 $ to get $ \dfrac{6k^5+45k^4+130k^3+189k^2+146k+45}{30} $. Step 1: Write $ 3k^2+9k+5 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator. Step 2: Multiply numerators and denominators. Step 3: Simplify numerator and denominator. $$ \begin{aligned} \frac{2k^3+9k^2+13k+9}{30} \cdot 3k^2+9k+5 & \xlongequal{\text{Step 1}} \frac{2k^3+9k^2+13k+9}{30} \cdot \frac{3k^2+9k+5}{\color{red}{1}} = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \left( 2k^3+9k^2+13k+9 \right) \cdot \left( 3k^2+9k+5 \right) }{ 30 \cdot 1 } \xlongequal{\text{Step 3}} \frac{ 6k^5+18k^4+10k^3+27k^4+81k^3+45k^2+39k^3+117k^2+65k+27k^2+81k+45 }{ 30 } = \\[1ex] &= \frac{6k^5+45k^4+130k^3+189k^2+146k+45}{30} \end{aligned} $$ |