Classify the following polynomials as polynomials in one variable, two variables etc.

(i) x² + x + 1

(ii) y³ – 5y

(iii) xy + yz + zx

(iv) x² – 2xy + y² + 1

(i) x² + x + 1 is a polynomial in one variable as it contains only one variable i.e. x.

(ii) y³ – 5y is a polynomial in one variable as it contains only one variable i.e. y

(iii) xy + yz + zx is a polynomial in three variable as it contains two variables i.e. x , y and z.

(iv) x² – 2xy + y² + 1 is a polynomial in two variables as it contains two variables i.e. x and y