How to solve a differential equation and the plug a number in for the resulting differential equation

I can do diff((1 + 5 * x^2 - 2 * x^3 + 8 * x^4) ^(1/8))), but I don't have an idea what to after

Answer 1

[David Goodmanson]

Hi Benjamin,

syms x
d = diff((1 + 5 * x^2 - 2 * x^3 + 8 * x^4) ^(1/8))
x0 = 8.8
val = double(subs(d,x0))

  val =
    0.2187

% this shows part of what is going on
dx0 = subs(d,x0)