polynomials
1. (2a^3b^-2)(-4a^2b^4)
18. a^2n^7/an^4
19. -y^3z^5/ y^2z^3
Apparently you want to simplify the expressions. I'll do #19.
y^3/y^2 = y
z^5/z^3 = z^2
So, you are left with -yz^2
Try the others. What do you get? If in doubt, show your work.