MATLAB: How do you do a derivative with a certain value

derivativesSymbolic Math Toolbox

My initial equation is f(x) = (3*x^5)-(x^3)+(2*x^2)+4 and when I derive that, I get f'(x)=15*x^4 – 3*x^2 + 4*x. How do I evaluate f'(x) when x = 1.7?

So far I have done this:

clear all, close all

syms x f = (3*x^5)-(x^3)+(2*x^2)+4; diff(f)

This gives me the derivative, but how do I find the value of f'(x) when I have a value for x?

Yianni - try using subs as

 syms x 
 f = (3*x^5)-(x^3)+(2*x^2)+4; 
 df = diff(f);
 result = double(subs(df,1.7));

You will need to create ‘f’ as a symbolic function (possible in R2012a and later versions).

Either of these will work:

syms f(x) x
f = x^2+4*x+5
df = diff(f)

or:

syms x
f(x) = x^2+4*x+5
df = diff(f)

Then, evaluating it when ‘x’ is 0 should be straightforward.

A = [1 2 4 6];
syms x
f(x) = x^2
sol = f(A)

gives:

f(x) =
 
x^2
 
sol =
 
[ 1, 4, 16, 36]