(a)9a^2+30a+25=(3a)^2+2*(3a)*5+5^2=(3a+5)^2
(b)9a^2+30a+25-25b^2+10b-1=(3a+5)^2-[(5b)^2-2*(5b)*1+1^2]
=(3a+5)^2-(5b-1)^2=(3a+5+5b-1)[3a+5-(5b-1)]=(3a+5b+4)(3a-5b+6)
(a) x^3-8=x^3-2^3=(x-2)(x^2+2x+2^2)=(x-2)(x^2+2x+4)
(b) x^3+x-10=(x^3-8)+(x-2)=(x-2)(x^2+2x+4)+(x-2)*1=(x-2)(x^2+2x+5)