5. (a-c)^3=a^2-2ac+c^2
6.(c+d)^3=c^3+3c^2d+3ad^2+d^3
7.(z-t)^3=z^3-3z^2t+3zt^2-t^3
8.(k+m)^3=k^3-3k^2m+3km^2-m^3
