# MATLAB HELP - Maclaurin series

1. Oct 4, 2006

### figgy111

MATLAB HELP!!! -- Maclaurin series

Hi, i have absolutely no programming experience with matlab and really need it. We have been assigned 2 problems using matlab and a bunch of others that don't need matlab. I was wondering if someone could show me what to do for the two needed to be done in matlab (or send a .m file if you have one/could create one); the questions are:

The Maclaurin series expansion for cos (x) is:

cosx = 1 - (x^2)/2 + (x^4)/4! - (x^6)/6! + (x^8)/8! - .....

Starting with the simplest version, cosx = 1, add terms one at a time to estimate cos(pi/3). After each term is added, compute the true and approximate percent relative errors. Use your pocket calculator to determine the true value. Add terms until the absolute value of the approximate error estimate falls below an error criterion conforming to two significant figures.

The other question is:

Use a centered difference approximation of O(h^2) to estimate the second derivative of the function f(x) = 25x^3 - 6x^2 + 7x - 88. Perform the evaluation at x = 2 using step sizes of h = 0.25 and 0.125. Compare your estimates with the true value of the second derivative. Interpret your results on the basis of the remainder term of the taylor series expansion.

2. Oct 5, 2006

### Andrew Mason

You don't need MatLab. You have just have to add the first few terms. You do this by replacing x by $\pi/3$ in the MacLaurin/Taylor series expansion and calculating the first few terms on a calculator. Calculate $cos(\pi/3)$ on a calculator. Compare the two. If the difference is less than .005 then you have the answer to two significant figures. If not, keep adding more terms until you get the difference down to less than .005.

AM

3. Oct 5, 2006

### Pythagorean

and if you're required to use matlab, what are you having trouble with? Do you understand AM's logic? Do you need help with the commands for the .m file?

I took a matlab class and I still use the program once in a while, if you can aska specific question, or PASTE your .m file here, I'll see what I can help you with.

4. Oct 5, 2006

### figgy111

yes we are required to use matlab

i did the first one alright the second one i had some trouble with. here is my .m file for that one i know its a little of but let me know. thanks in advance

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