pk+p^2-2pk-2k-2p= -pk+p^2-2k-2p
ab+a-ac-bc+bc+b-a-b=ab-ac
а) p(k+p)-2k(p-1)-2p=p*k+p^2-2k*p+2k-2p=p^2-p*k+2k-2p=p(p-k)-2(p-k)=(p-k)*(p-2)
б) a(b+1)-c(a+b)+b(c+1)-(a+b)=ab+a-ca-cb+bc+b-a-b=ab-ac=a(b-c)
