x²-5x+3
=x²-5x+25/4-25/4+3
=(x-5/2)²-13/4
=(x-5/2+√13/2)(x-5/2-√13/2)
x³+9+3x²+3x
=(x³+3x²)+(3x+9)
=x²(x+3)+3(x+3)
=(x+3)(x²+3)