According to the concept,
The relation between rectangular coordinates and polar coordinates are:
[tex]\begin{gathered} x^2+y^2=r^2 \\ \beta=\tan ^{-1}\frac{y}{x} \end{gathered}[/tex]
Then,
x = 9, and y = -9
So,
[tex]\begin{gathered} x^2+y^2=r^2 \\ 9^2+(-9)^2=r^2 \\ 81+81=r^2 \\ 162=r^2 \\ r=12.7 \end{gathered}[/tex]
And,
[tex]\begin{gathered} \beta=\tan ^{-1}\frac{y}{x} \\ \beta=\tan ^{-1}\frac{-9}{9} \\ \beta=\tan ^{-1}(-1) \\ \beta=-45^{\circ} \end{gathered}[/tex]
Hence, the polar coordinate is shown below:
[tex](12.7,-45^{\circ})[/tex]
