Let's assume that ,are the roots of the equation , a,b,c belong to R and a is not zero. Then if we name S the sum and P the multiple of ,we have:
and
So,

The above formulas relate the roots of
an equation with their coefficients. There are useful for various practical
and theoretical problems and are valid even when D<0 in which is case
the equation has two conjugate complex solutions. They are known as the
Vieta formulas.
It is true that:
So, if +=S
and =P
then the numbers ,
are the roots of the equation .