How to calculate the differential coefficient in c

Question

Thanks a lot people for your help so far but I made a big mistake I need the derivation of a function at a specific point!

I have to calculate the first derivation of a function and I really have no clue how to get there. If I just had to calculate it for a function with just a X^1 I would know how to but I'm really stuck here.

Old Stuff: A function can look like 2*x^2+1.

The method has to look like this: double ab(double (f)(double),double x) and my professor gave us the hint that we might should use the function: (f(x0+∆x)−f(x0))/((x0+∆x)−x0).

Sorry for my bad English and thanks for any kind of hint or tip in advance.

Answer 1

this sample will get you started :

#include<stdio.h>
#include <stdlib.h>


float func(float x)
{
    return(2*x*x + 1);
}

int main(){
    float h=0.01;
    float x;
    float deriv, second;

    printf("Enter x value: ");
    scanf("%f", &x);
    // derivative at x is the slope of infinitely small
    // line of the function 

    deriv = (func(x+h) - func(x))/h; // I assumed the length to be h

    //for second derivative you can use:
    second = (func(x+h) - 2*func(x) + func(x-h))/(h*h);

    printf("%f\n", deriv);
    return 0;
}

Answer 2

The idea is approximate the first derivative of f() at x with the slope of the secant line through the points (x, f(x)) and (x+∆x, f(x+∆x)).

The Wikipedia article should get you started.