5x^3-x^2-45x-9=0
x^2(5x - 1) -9(5x + 1) = 0
I think you have a typo, and my guess is that the -9 is +9
that would make it
x^2(5x - 1) -9(5x - 1) = 0
(5x-1)(x^2 - 9) = 0
(5x-1)(x+3)(x-3) = 0
x = 1/5, -3, +3
factor by grouping
5x^3-x^2-45x-9=0
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