This is because . In short, squaring a negative leads to a positive.
This means that regardless of what theta is, the distance from the origin to the point will always be 1.
The point means that and .
So which is simply . This is the equation for the unit circle.
The unit circle is a special circle with radius 1 and centered at the origin.
All such points on the unit circle are exactly 1 unit away from the origin.
The point is located on the unit circle.