Find a polynomial, which, when added to the polynomial 5x2–3x–9, is equivalent to: 0

3 answers

well,
5 + -5 = 0
-3 + 3 = 0
...
5x^2-3x-9
Huh? The original polynomial?
You want

(5x^2-3x-9)-(5x^2-3x-9) = 0

now just change the signs of the 2nd polynomial so you can add it instead of subtracting.