first forward and backward central diference

Hi, I have a task to do by diference of those formulas someone help me? input values are specified they get when I have done.

dy1=((f(x+h)-f(x-h))/(h))-1/2*h;
dy2=(((-3*f(x))+4*f(x+h)-f(x+2*h))/(2*h))+1/3*h^2;
dy3=((f(x+h)-f(x-f))/2*h)-1/6*h^2;

[Adam]

for example, those equations:

f(x)=(x^2)+3

[Titus Edelhofer]

I understand the task. But I have not found a question?

[Adam]

I do not know what I should do next, the result is some kind of strange

t=0.8;

h = 0:t:10^-5;

x=5;

f(x)=(x^2)+3;

dy=((f(x+h)-f(x-h))/(h))-1/2*h

Answer 1

[Titus Edelhofer]

Hi,

o.k., let's start with the h:

0:t:10^-5

will be the zero. Start with e.g.

h = 0.01;

Take a look at the chapter about defining functions (or search the doc for "function handles" on how to define f.

Titus

Answer 2

[Walter Roberson]

Algebra. What is f(x)=(x^2)+3 evaluated at (x+h) ? And at (x-h) ? And so on. Simplify and you get down to a nice formula.