
How do change the default period in a sine or cosine wave to π or 3π instead of 2π
OK, so in the trigonometry graph I am able to plot phase shift and vertical shifts of sine and cosine waves.
However, I am not able to get it to do a different period, such as π. The default period is of course 2π. But how can I get it to do 1/2 or 3π or something crazy like that?
Thanks.
Rob

Hi Rob,
You would find it interesting and hopefully enlightening to experiment with a variety of ways to transform the sine function. Consider starting with a function expressed as y = a sin (bx + c) + d. Use initial parameter values of a=1, b=1, c=0, and d=0 so that your initial expression is equivalent to y = sin (x). Then experiment with changing each of the parameters in turn to see its effect  but first, before changing a parameter, think carefully about the effect it will have and make a prediction about how the graph will change. The objective, of course, is to develop a clear understanding and explanation of the transformation that results from changing each parameter, and as a result to be able to create (for instance) a sine wave with an amplitude of 0.5, centered on the line y = 2, and with maximum values at x=0 and at x=pi/2. (In other words, given an amplitude, vertical offset, period, and phase shift, you should be able to immediately change the parameters to produce the desired graph.)
Scott

Stek,
I go to Number  Calculate and I try to put in y=sin(bx+c)+d and it doesn't let me. Do you use Number  Calculate to make this equation? I am able to manipulate amplitude, but not phase shift, verticle shift or period. So I need more detailed instructions on how to make Sketchpad do this operation.
OK, I have managed to get phase shift and verticle shift by doing sin(x+π) but I still can't change the period. If I do something like sin(3π) I just get a straight line, or sin(π/2) still a straight line.
Last edited by Robwinfield; 07012012 at 06:46 PM.

Hi Rob,
You'll need to create parameters for the coefficients and constants (b, c, d, n). Choose NumberNew Parameter.
A couple of resources may be helpful. The first is this Algebra tutorial––it isn't about Sine curves, but it will get you started using parameters with functions: http://learningcenter.dynamicgeometry.com/x24.xml
Also, on the first and third Tuesday of each month, we offer free Sketchpad webinars. These are a nice way to get a focused Sketchpad "lesson" from an experienced Sketchpad user. You can see the schedule here: www.keycurriculum.com/webinars.
Finally, we do have sixweek moderated online courses that will guide you in digging more deeply into Sketchpad. These aren't free, but they are very reasonably priced.
Happy sketching!
Elizabeth

Thanks for the nice information in this post dear...
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