I will use cubic polynomial to explain this.Let the graph of the polynomial cuts the X axis at , a, b and c.Suppose all the three roots of the cube are Real.
So, it has three roots equal to a, b and c.
Equation of Cubic Polynomial is given by:
= (x-a)(x-b)(x-c)
= [x² - (a+b)x + a b](x-c)
= x²(x -c)-x(a+b)(x-c)+ab(x-c)
= x³-x²c- (x²-xc)(a+b)+a b x - a b c
= x³ - x² c-x² a - x² b+a c x + b c x+a b x - a b c
=x³-x²(a+b+c)+x(a b+b c+ca)-a b c
The factors a, b and c can be any rational number in the form of
For example ,the roots of the cubic polynomial are 1, -1 and 3.