Which of the following is not a monomial?

Options

A. `2x^2+1`
B. `3x^4`
C. `a b`
D. `x^2y`

Answer

To determine which of the following options is not a monomial, we first need to understand what a monomial is. A monomial is defined as a polynomial that consists of only one term. This means it cannot contain addition or subtraction operators.

Now, let's analyze each option step by step:

1. **Option A: 2x² + 1**
- This expression contains an addition operator (+).
- Since it has more than one term (2x² and 1), it is not a monomial.

2. **Option B: 3x⁴**
- This expression contains only one term (3x⁴).
- There are no addition or subtraction operators present, so this is a monomial.

3. **Option C: ab**
- This expression also contains only one term (ab).
- There are no addition or subtraction operators present, so this is a monomial.

4. **Option D: x²y**
- This expression contains only one term (x²y).
- There are no addition or subtraction operators present, so this is a monomial.

After analyzing all the options, we conclude that:

- **Option A (2x² + 1)** is not a monomial because it contains an addition operator and has more than one term.

### Final Answer:
**Option A: 2x² + 1 is not a monomial.**

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