x三次方+3x二次方+3x+2
=x^3+3x^2+3x+2
=(x^3+3x^2+2x)+(x+2)
=x(x+1)(x+2)+(x+2)
=(x^2+x+1)(x+2)
x四次方-7x二次方+9
令x^2=t
t^2-7t+9
=[t-(7-√13)/2]*[t-(7+√13)/2]