Step 1: First we have to write polynomials in descending order.

$$ \begin{aligned} P(x) &= 2x^2+x-1 \\ Q(x) &= x+3 \\ \end{aligned} $$

We can multiply polynomials by using a GRID METHOD

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

$$ \begin{darray}{|c|c|c|c|}\hline & \color{blue}{2x^2} & \color{blue}{x} & \color{blue}{-1} \\ \hline \color{blue}{x} & & & \\ \hline \color{blue}{3} & & & \\ \hline \end{darray} $$

Fill in each empty box by multiplying the intersecting terms.

$$ \begin{darray}{|c|c|c|c|}\hline & \color{blue}{2x^2} & \color{blue}{x} & \color{blue}{-1} \\ \hline \color{blue}{x} & \color{orangered}{2x^3} & \color{orangered}{x^2} & \color{orangered}{-x} \\ \hline \color{blue}{3} & \color{orangered}{6x^2} & \color{orangered}{3x} & \color{orangered}{-3} \\ \hline \end{darray} $$

Combine like terms:

$$ 2x^3 + x^2 + 6x^2-x + 3x-3 = \\ 2x^3+7x^2+2x-3 $$

Polynomial Operations Calculator