x³ + 5x² = 9x + 45
x²(x+5)=9(x+5)
x²(x+5)-9(x+5)=0
(x+5)(x²-9)=0
(x+5)(x-3)(x+3)=0
x+5=0, x-3=0, x+3=0
x=-5, -3 и 3
