Question

Find a third-degree polynomial equation with rational coefficients that has roots –4 and 2 + i

Answer 1

If it has rational coefients and is a polygon
if a+bi is a root then a-bi is also a root

the roots are -4 and 2+i
so then 2-i must also be a root


if the rots of a poly are r1 and r2 then the factors are
f(x)=(x-r1)(x-r2)

roots are -4 and 2+i and 2-i

f(x)=(x-(-4))(x-(2+i))(x-(2-i))
f(x)=(x+4)(x-2-i)(x-2+i)
expand
f(x)=x³-11x+20