Beginner question on trigonometry proofs...

Discussion in 'MATLAB' started by Katy, Feb 12, 2006.

  1. Katy

    Katy Guest

    I am new to MATLAB and have yet to find any information on verifying
    trigonometric identities. Namely, how do I make a program that asks a
    user to enter a value of theta in degrees. I believe I need the input
    function for this? Also, the disp function. How do I use a loop
    function for this since I need it to give answers without repeating
    itself. I need my program to verify sin(2theta) =
    2sin(theta)cos(theta) for several values of theta by computing and
    displaying both sides of the equation and the difference between
    them. As I said, I'm new to MATLAB and any help would be appreciated!
    Katy, Feb 12, 2006
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  2. Katy

    us Guest

    <SNIP charming little homework problem...

    one of the many solutions

    % copy/paste this section into your command window
    % exit loop with a CTRL-C sequence
    while true
    thd=input('enter theta in deg < ');
    'theta %10.3f\n',...
    'eq 1 %30.23f\n',...
    'eq 2 %30.23f\n',...
    'diff %30.23f\n'],...

    note that there are FP issues, eg,
    try with 45 and 48
    us, Feb 12, 2006
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  3. Katy

    Katy Guest

    Thanks so much! If it wouldn't be too much trouble, could you explain
    what the different steps of code means? I am familiar with assigning
    variables a value but I am not familiar with the portion below
    txt=sprintf. Could I use this same thing for another trigonometric
    proof..of course changing values, etc? Thanks again!
    Katy, Feb 12, 2006
  4. Katy

    us Guest

    <SNIP down to basic questions...

    as this command, typed at the command prompt in the command window as
    shown below

    help sprintf

    shows, the above syntax serves the purpose to write formatted data
    (here: your input and various results) to a char array (also known as
    string), which is ready for display as coded in the snippet

    us, Feb 12, 2006
  5. Katy

    Katy Guest

    Thanks again...I have one more question. I hope you don't mind my
    simple questions. What is the significance of the numbers, dots, and
    f\n,within these rows?
    : 'theta %10.3f\n',...
    and do these numbers change if I were to do this for
    Katy, Feb 12, 2006
  6. Katy

    us Guest

    <SNIP sprintf-formatting trivia...
    according to
    help sprintf
    you see that these numbers aren't but simple instructions on how the
    corresponding data should be turned into a character representation,
    eg, look at this

    disp(sprintf('pi is %f',pi));
    disp(sprintf('pi is %g',pi));
    disp(sprintf('pi is %30.20f',pi));
    disp(sprintf('pi is %s',sprintf('%.10f',pi)));
    % again, scrutinize
    % help sprintf
    % doc sprintf

    no - not necessarily, that is - it all depends on how you want your
    output to look like (eg, precision, additional information for the
    user, etc)
    us, Feb 12, 2006
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