1. The problem is to understand how we determine that an angle is not negative. 2. Angles are typically measured from a reference line, usually the positive x-axis, in a counterclockwise direction for positive angles and clockwise for negative angles. 3. If an angle is given or measured in a context where the direction or quadrant is specified, we can identify whether it is positive or negative. 4. For example, if an angle is described as rotating counterclockwise from the positive x-axis, it is positive. 5. If the problem or context does not mention a negative rotation or clockwise direction, the angle is assumed positive. 6. Additionally, angles are often given in the range $0^\circ$ to $360^\circ$ or $0$ to $2\pi$ radians, which are positive measures. 7. Therefore, unless explicitly stated or implied by direction, angles are considered positive by default.