Write 'T' for True and 'F' for False.
A statement is not a declarative sentence.

Answer

To determine the truth value of the statement "A statement is not a declarative sentence," we will analyze the definitions and concepts involved.

### Step-by-Step Solution:

1. **Understanding the Definition of a Statement**:
- A statement, in mathematical reasoning, is defined as a declarative sentence that can either be true or false, but not both at the same time.

2. **Analyzing the Given Statement**:
- The statement we need to evaluate is "A statement is not a declarative sentence."

3. **Contradicting the Definition**:
- According to the definition, a statement is indeed a declarative sentence. Therefore, saying "A statement is not a declarative sentence" contradicts the established definition.

4. **Determining the Truth Value**:
- Since the given statement contradicts the definition of what a statement is, it cannot be true. Thus, the truth value of the statement "A statement is not a declarative sentence" is false.

5. **Final Answer**:
- Therefore, we write 'F' for False.

### Summary:
The truth value of the statement "A statement is not a declarative sentence" is False (F) because it contradicts the definition of a statement.

---