A4. 25z^4 -b^6 = (5z² -b^3)(5z² +b^3)
A6. 5c(x -y) /15cz =(x -y)/3z
A7. ab(ab +1) +c(ab +1) = (ab +1)(ab +c)
A8. (y -2)(y +2) /y(y +2) = (y -2) / y
A9. 64a² -16ab +b² = (8a -b)²
A10. -3x(4x² +1 +4x) = -3x(4x² +4x +1) = -3x(2x +1)² = -3x(2x +1)(2x +1)