Find a polynomial, which, when added to the polynomial 5x^2–3x–9, is equivalent to
x^2-5x+6

So this is easy counting
so 5x^2-3x-9
we have 5 x^2's
-3 x's
-9

wat do we add to that to get
1 x^2's
-5 x's
+6
so we do each
5x^2+what=1x^2
subtract 5x^2
from both sides
what=-4x^2
first is -4x^2

then we have -3x to -5x
-3x+what=-5x
add 3x to both sides
what=-2x
second is -2x

-9 to 6
-9+ what=6
ad d9
what=15
last is 15
thereffor add -4x^2-2x+15