The first derivative of 8√x (which can be written 8x½) is (½)8x-½=4/√x.
The second derivative is (-½)4x-3/2=-2/√x3.
The third derivative is (-3/2)(-2)x-5/2=3/√x5.
The fourth derivative is (-5/2)3x-7/2=-(15/2)/√x7.
The fifth derivative is (105/4)/√x9.
The nth derivative is (-1)n+1((1)(3)(5)...(2n-3)/2n-3)/√x2n-1, where integer n>1.
For example, n=3 gives us (1)(3)/√x5=3/√x5; n=2 gives us -(1/½)/√x3=-2/√x3.