The first thing to do in this case is to write the polynomial in a factored form for the roots.
We have then:
(x-5) * (x + 4) = 0
Then, rewriting the quadratic equation:
(x-5) * (x + 4)
x ^ 2 + 4x -5x -20
x ^ 2 -x -20
answer:
the quadratic equation whose roots are 5 and -4, and whose leading coefficient is 1 is
x ^ 2 -x -20
