-9x^3-72x^2+36=3x^3+x^2-3x+8 Add 9x^3 to both sides.
-72x^2 + 36 = 3x^3 + 9x^3 + x^2 - 3x + 8 Add 72x^2 to both sides
36 = 12x^3 + 73x^2 - 3x + 8 Subtract 36 from both sides.
0 = 12x^3 + 73x^2 - 3x - 28
It does factor, but it is not very nice.
(x + 6.06)(x - 6.09)(x + 0.632)
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