Fill in the following blanks :
In every triangle, an exterior angle + adjacent interior angle = . . . degrees.

Answer

To solve the question, we need to understand the relationship between an exterior angle of a triangle and its adjacent interior angle.

**Step-by-Step Solution:**

1. **Understanding the Triangle**:
- Let's consider a triangle ABC. In this triangle, let angle A be an interior angle.

2. **Identifying the Exterior Angle**:
- The exterior angle is formed when one side of the triangle is extended. For instance, if we extend side BC, we can form an exterior angle at vertex A, which we will call angle D.

3. **Identifying the Adjacent Interior Angle**:
- The adjacent interior angle to the exterior angle D is angle A itself.

4. **Using the Straight Line Property**:
- The exterior angle D and the adjacent interior angle A together form a straight line. Therefore, the sum of these two angles must equal 180 degrees. This is because angles on a straight line always add up to 180 degrees.

5. **Writing the Equation**:
- We can express this relationship mathematically as:
\[ \text{Exterior Angle (D)} + \text{Adjacent Interior Angle (A)} = 180 \text{ degrees} \]

6. **Conclusion**:
- Therefore, we can fill in the blank in the question: In every triangle, an exterior angle + adjacent interior angle = **180 degrees**.

**Final Answer**: 180 degrees.

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