Zero of a function
In other words, a "zero" of a function f is a value for x that produces a result of zero ("0"). For example, consider the function f defined by the formula
f has a root at 3 since
If the function maps real numbers to real numbers, its zeros are the x-coordinates of the points where its graph meets the x-axis. An alternative name for such a point (x,0) in this context is an x-intercept.
The concept of complex numbers was developed to handle the roots of cubic equations with negative discriminants (that is, those leading to expressions involving the square root of negative numbers). Complex numbers also occur as zeros of quadratic equations with negative discriminants.
Computing roots 
Polynomial roots 
Every real polynomial of odd degree has at least one real number as a root. Many real polynomials of even degree do not have a real root, but the fundamental theorem of algebra states that every polynomial of degree n has n complex roots, counted with their multiplicities. The non-real roots of polynomials with real coefficients come in conjugate pairs. Vieta's formulas relate the coefficients of a polynomial to sums and products of its roots.