According to the fundamental theorem of algebra, a polynomial has the 
number of zeros equivalent to the degree of the polynomial.
A quadratic equation is of degree 2 and hence has 2 zeros.
A complex zero is of the form [tex]a\pm bi[/tex] which represents two zeros: a + bi and a - bi.
Thus,
 since a quadratic equation has only 2 zeros, a quadratic equation with a
 complex zero already have two zeros and hence will not have any other 
zero.