X³+5x²+3x-9 =x(x^2+4x+3)+x^2-9=x(x+3)(x+1)+(x+3)(x-3)=(x+3)[x(x+1)+x-3]=(x+3)[x^2+2x-3]=(x+3)^2(x-1) x四次方—7x²+1=(x^2-1)^2-5x^2=(x^2-1+√5x)(x^2-1-√5x) .