Question

Convert the rectangular coordinates (-9, 3V3) into polar form. Express the angle

Answer 1

Answer:

$(6\sqrt{3},\,\frac{5\pi}{6})$

Step-by-step explanation:

The radius  r  can be found from the relationship

 $r^2=x^2+y^2\\r^2=(-9)^2+(3\sqrt{3})^2\\r^2=81+27=108\\r=\sqrt{108}\\r=6\sqrt{3}$

The point is in Quadrant II (-, +), so use the inverse cosine function to find the angle.

$\cos{\theta}=\frac{x}{r}=\frac{-9}{6\sqrt{3}}\\\cos{\theta}=-\frac{9}{6\sqrt{3}} \cdot \frac{\sqrt{3}}{\sqrt{3}}\\\cos{\theta}=-\frac{9\sqrt{3}}{6\cdot3}\\\cos{\theta}=-\frac{\sqrt{3}}{2}\\\\\cos^{-1}\frac{-\sqrt{3}}{2}}=\frac{5\pi}{6}$

See the attached image.