Rectangular → polar, third quadrant

A point in the third quadrant: $\displaystyle x = -3$, $\displaystyle y = -2.5$. Watch the signs. Press , then and type 3 for $\displaystyle -3$. Press and , then and type 2.5. Press and : $\displaystyle r$ is 3.905124838. Press and for $\displaystyle \theta$: −140.1944289 degrees. The calculator measures the angle from the positive $\displaystyle x$-axis and keeps it between $\displaystyle -180^{\circ}$ and $\displaystyle +180^{\circ}$, so $\displaystyle -140.19^{\circ}$ clockwise is the same direction as $\displaystyle 219.81^{\circ}$ anticlockwise. Always check which quadrant your point is in.

▶ Watch this step in the video (49:59)