(i) 3x^{2} -4x+15 is a polynomial of one variable x.

(ii) y^{2} -2√3 is a polynomial of one variable y.

(iii) 3√x +√2x is not a polynomial as the exponents of 3√x is not a positive integer.

(iv) x - 4/x is not a polynomial as the exponent of -4/x is not a positive integer.

(v) x^{12} + y^{3} + t^{50 }is a polynomial of three variables x, y, t.