It was shown on the page of Literka Polynomials that the values cos(2*pi/13), cos(4*pi/13), cos(6*pi/13),
cos(8*pi/13), cos(10*pi/13), cos(12pi/13) are roots of the polynomial P(x) equal
Polynomial P(x) is a product of two polynomials Q(x) and R(x)
P(x)=Q(x)*R(x)
where polynomial Q(x) is equal
and polynomial R(x) is equal
Using formulas of the page of Literka cubic formulas we can find roots of polynomials Q(x) and R(x). We
receive: