Question

Find a third-degree polynomial equation with rational coefficients that has roots –5 and 6 + i.

Answer 1

The coefficients of the polynomial are rational, which means that any non-real roots occur alongside their complex conjugates. In this case, 6+i is a root, so 6-i is also a root.

So the simplest polynomial you can build with these roots is

(x - (-5)) (x - (6 + i )) (x - (6 - i )) = x ^3 - 7x ^2 - 23x + 185

(first choice)