If the sum of two adjacent angles is `180^@`, then the ___ arms of the two angles are opposite rays.

Answer

To solve the question, we need to understand the relationship between adjacent angles and their arms when their sum is 180 degrees.

### Step-by-Step Solution:

1. **Understanding Adjacent Angles**:
- Adjacent angles are two angles that share a common vertex and a common arm but do not overlap.

2. **Given Condition**:
- The problem states that the sum of the two adjacent angles is 180 degrees. This means that together, they form a straight angle.

3. **Visualizing the Angles**:
- If we visualize two adjacent angles, let’s denote them as ∠AOB and ∠BOC, where O is the common vertex, and OB is the common arm.
- Since the sum of these angles is 180 degrees, we can say that the angles together form a straight line.

4. **Identifying the Arms**:
- The arms of the angles are OA (for ∠AOB) and OC (for ∠BOC).
- The common arm is OB, while OA and OC are the non-common arms.

5. **Understanding Opposite Rays**:
- Opposite rays are two rays that share a common endpoint and extend in opposite directions.
- In this case, OA and OC extend in opposite directions from point O.

6. **Conclusion**:
- Therefore, the non-common arms of the two angles (OA and OC) are opposite rays.

### Final Answer:
The non-common arms of the two angles are opposite rays.

---