36a^3(x-y)^2/27a(y-x)
=36a³(x-y)²/[-27a(x-y)]
=-4/3*a²(x-y)
,6(-a)^3/-4a^2b
=-6a³/(-4a²b)
=-2a²*3a/(-2a²*b)
=3a/b