The command

`Maximize[{Sqrt[2 x + 13] + (3 y + 5)^(1/3) + (8 z + 12)^(1/4), x + y + z == 3&&{x,y,z} >= 0}, {x, y, z}] `

is running without any response on my comp for hours (as well as many other Mathematica commands). This optimization problem is quite standard and easily solved by Lagrange multipliers

`L=Sqrt[2x+13]+(3y+5)^(1/3)+(8z+12)^(1/4)-t*(x+y+z-3); `

For simplicity the conditions `{x,y,z}>=0`

are not taken into account.

`Reduce[D[L, x] == 0 && D[L, y] == 0 && D[L, z] == 0 && D[L, t] == 0, {x, y, z, t}, Reals] `

`x == 3/2 && y == 1 && z == 1/2 && t == 1/4`

The Hessian of `L`

at this point is easily found by

`M = {{D[L, x, x], D[L, x, y], D[L, x, z], D[L, x, t]}, {D[L, y, x], D[L, y, y], D[L, y, z], D[L, y, t]}, {D[L, z, x], D[L, z, y], D[L, z, z], D[L, z, t]}, {D[L, t, x], D[L, t, y], D[L, t, z], D[L, t, t]}} /. {x -> 3/2, y -> 1, z -> 1/2, t -> 1/4} `

Next, the result of

`Resolve[ForAll[{a,b,c,d}, ({a,b,c,d}.M).{a,b,c,d} <= 0], PositiveReals] `

`True`

states this is the maximum point (local and global) since the quadratic form `({a,b,c,d}.M).{a,b,c,d}`

takes nonpositive values on the positive reals. Is there anoter way to symbolically solve this optimization problem?