Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer:

(i) 3x²-4x+15

(ii) y²+2

(iii) 3+x

(iv) x-

(v) x¹²+y³+t⁵⁰

(i) 3x²-4x+15 is a polynomial of one variable x.

(ii) y²+2_{is a polynomial of one variable y.}

(iii) 3+x is not a polynomial as the exponent of 3_{is not a positive integer.}

(iv) x - is not a polynomial as the exponent of - is not a positive integer.

(v) x¹²+y³+t⁵⁰ is a polynomial of three variables x, y, t.