First octant means xgt=0, ygt=0, zgt=0. The formula y=27/8 x^3 may be written as y=(3/2 x)^3. We need the (simple) inverse formulas, too: x=2/3 root(3)(y), z=1-y/2.
Because zgt=0 we see ylt=2 and therefore xlt=2/3 root(3)(2). Also, z=1-y/2lt=1. Now we are ready to write the integral in different orders of variables.
If x is fixed, y can be between (3/2 x)^3 and 2 in xy plane z=0. For fixed x and y we see z can be between 0 and 1-y/2, i.e. the integral becomes
int_(x=0)^(x=2/3 root(3)(2)) dx int_(y=(3/2 x)^3)^(y=2) dy int_(z=0)^(z=1-y/2) dz(1) = int_(x=0)^(x=2/3 root(3)(2)) int_(y=(3/2 x)^3)^(y=2) int_(z=0)^(z=1-y/2) 1 dz.
If we start from y it can be from 0 to 2, then x can be from 0 to 2/3 root(3)(y) and z can be from 0 to 1-y/2. The integral is
int_(y=0)^(y=2) int_(x=0)^(x=2/3 root(3)(y)) int_(z=0)^(z=1-y/2) 1 dy dx dz.
And if we start with z, it can be from 0 to 1, then y can be from 0 to 2-2z and x from 0 to 2/3 root(3)(y), i.e.
int_(z=0)^(z=1) int_(y=0)^(2-2z) int_(x=0)^(x=2/3 root(3)(y)) 1 dz dy dx.
It is not that simple to sketch V but I tried. :)
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