Verified answer

а)с^2-16c =с(с-16)

b)3a^2-16ab+3b^2=1/3(3a-8b+b*sqrt(55))(3a-8b-b*sqrt(55))

c)81a^4-1 =(9a^2-1)(9a^2+1)=(3a-1)(3a+1)(9a^2+1)

d)y^2-x^2-6x-9=y^2-(x+3)^2=(y-x-3)(y+x+3)

а) с^2-16c=с*(с-16);

b) 3a^2-16ab+3b^2=1/3*(3a-8b+b*V55)*(3a-8b-b*V55);

c) 81a^4-1=(9a^2-1)(9a^2+1)=(3a-1)*(3a+1)*(9a^2+1);

d) y^2-x^2-6x-9=y^2-(x+3)^2=(y-x-3)*(y+x+3).