0
$\begingroup$

This may be somewhat of a basic question, but I need to know... I'm trying to find the minimum and maximum for the following: $$y = \frac{\cos 3x}{5}+\sin 3x$$

How is this done on a TI-83?

  • 0
    Thanks, Thomas, I figured out what was wrong: I had one of the plots under stat plots turned on so it wouldn't let me graph...2012-10-23

1 Answers 1

2
  • You enter the function as (for example) a $Y_1$ (using the [y=] button).
  • You try to sketch the graph and adjust the window so that it shows the minimum or maximum that you want to find. (Hint: try for example $x_{min} = -5$, $x_{max} = 5$, $y_{min} = -2$, $y_{max} = 2$)

  • You click [2nd] [calc] and choose (say) minimum.

  • You put the cursor to the left of the minimum and click enter. You put it to the right and click enter.

  • You move the cursor so that it is close to where the minimum is and you click enter.

Note i your case, you will have infinitely many maximums and minimums since he function is periodic. When you find say a minimum, then you can add any (integer) multiple of $\frac{2\pi}{3}$ to get the other minimums. This should be clear from the graph.

  • 0
    I'm having a problem...when I plug cos(3X/5+sin(3X)) into y1 I get a window range error?2012-10-23
  • 0
    @Brandt: From the way that you had written things, I assumed that your function was $y = \cos(3x)/5 + \sin(3x).$ To correct the window issue press [window] and set the min and max values to what I have suggested in my answer.2012-10-23
  • 0
    you're right; I wrote the function incorrectly. But even after correcting that and setting the min and max values to what you suggested I still get an error, this time an "invalid dimensions" error...2012-10-23
  • 0
    What are the min and max values under [window] ?2012-10-23
  • 0
    Xmin=-5, Xmax=5, Xscl=-2 (I don't know how to clear this one), Ymin=-2, Ymax=2, Yscl=.1 and Xres=12012-10-23
  • 0
    Ahh I see. The Xscl needs to be a positive number. With the cursor select this and change it so say 1.2012-10-23
  • 0
    let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/6216/discussion-between-thomas-and-brandt)2012-10-23
  • 0
    chat doesn't seem to be working for me and IDKY but after changing the Xscl to 1 I still get the same error2012-10-23
  • 0
    If you still get the "window error" then I don't really know.2012-10-23
  • 0
    You might try to reset the calculator. You can do this under the [mem] button.2012-10-23