Which angle is included between the side DE and EF of `DeltaDEF`?

Options

A. `angleD`
B. `angleE`
C. `angleF`
D. can't be determined

Answer

To find the angle included between the sides DE and EF of triangle DEF, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Triangle**: We start by identifying the triangle DEF. We can visualize or draw the triangle with vertices D, E, and F.

2. **Label the Sides**: Next, we label the sides of the triangle. The side DE connects points D and E, and the side EF connects points E and F.

3. **Determine the Included Angle**: The angle that is included between the two sides DE and EF is the angle that is formed at vertex E. This is because angle E is the angle that opens between the two sides DE and EF.

4. **Name the Angle**: The angle at vertex E can be referred to in different ways. It can be denoted as:
- Angle DEF
- Angle E (the simplest form)
- Angle FED

5. **Conclusion**: Therefore, the angle included between the sides DE and EF of triangle DEF is angle E.

### Final Answer:
The angle included between the side DE and EF of triangle DEF is angle E.

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