We can multiply polynomials by using a GRID METHOD

Write one of the polynomials across the top and the other down the left side.

$$ \begin{darray}{|c|c|c|c|}\hline & \color{blue}{20x^2} & \color{blue}{200x} & \color{blue}{320} \\ \hline \color{blue}{x^2} & & & \\ \hline \color{blue}{9x} & & & \\ \hline \color{blue}{18} & & & \\ \hline \end{darray} $$

Fill in each empty box by multiplying the intersecting terms.

$$ \begin{darray}{|c|c|c|c|}\hline & \color{blue}{20x^2} & \color{blue}{200x} & \color{blue}{320} \\ \hline \color{blue}{x^2} & \color{orangered}{20x^4} & \color{orangered}{200x^3} & \color{orangered}{320x^2} \\ \hline \color{blue}{9x} & \color{orangered}{180x^3} & \color{orangered}{1800x^2} & \color{orangered}{2880x} \\ \hline \color{blue}{18} & \color{orangered}{360x^2} & \color{orangered}{3600x} & \color{orangered}{5760} \\ \hline \end{darray} $$

Combine like terms:

$$ 20x^4 + 200x^3 + 180x^3 + 320x^2 + 1800x^2 + 360x^2 + 2880x + 3600x + 5760 = \\ 20x^4+380x^3+2480x^2+6480x+5760 $$

Polynomial Operations Calculator