1) ............=k²(a-c)+k(a-c)-(a-c)=(a-c)(k²+k-1)
2) ............=k²(a+c)-k(a+c)+(a+c)=(a+c)(k²-k+1)
3) .............=k²(a+y+c)+k(a+y+c)=(a+y+c)(k²+k)
4) ............=5ak(k-2)-y(k-2)-(k-2)=(k-2)(5ak-y-1)
5) ............=6ay(2-c)-3ac(2ay-c)+(2ay-c)=(2ay-c)(6ay-3ac+1)