Classify the following polynomials as polynomials in one variable, two variables etc.
(1) `x^(2)+x+1` `" "`(ii) `y^(3)-5y`
(iii) `xy+yz+zx` `" "`(iv) `x^(2)-2xy+y^(2)+1`

Explanation

To classify the given polynomials, we will analyze each polynomial based on the number of variables it contains.

### Step-by-Step Solution:

1. **Identify the first polynomial: `x^2 + x + 1`**
- This polynomial contains only the variable `x`.
- Since it has only one variable, it is classified as a **polynomial in one variable**.

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