b) notam a^2+a=x
x(x-2)+1=x^2-2x+1=(x-1)^2=(a^2+a-1)^2
c)=x^2+4x+4=(x+2)^2
d)=x^3+2x^2-3x-6x-18=x(x^2+2x-3)-3(x+3)=x(x-1)(x+3)-6(x+3)=
(x+3)(x^2-x-6)=(x+3)(x-3)(x+2)=(x^2-9)(x+2)
e)=1-x+x^2-x^3=(1-x)+x^2 *(1-x)=(1-x)(1+x^2)
Ma mai gandesc si la a) (nu-i dau de cap)
