This page presents a calculator, solving problem of finding real roots of polynomials. That means, the calculator is solving the following equation
an x n + an-1 x n-1 . . . + a1 x + a0 = 0
Roots of low order polynomials can be expressed in form of more or less complicated formula. But there is no formula for polynomials of degree 5 or higher (n ≥ 5). In such cases, different algorithms are to be employed in to find approximation or roots.
What you should know about polynomials
(but you don't have to, if you use the calculator)