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HP Forum Archive 02

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Parametric plots on the 48
Message #1 Posted by Eric on 18 Apr 2000, 6:00 p.m.

Can someone help me, i lost my hp manuel and i cant figure out how to make parametric plots. i know how to get into the parametric mode but once i type the function in i get no graph of the function. im sure there is something im doing wrong. can someone please explain?

Re: Parametric plots on the 48
Message #2 Posted by William L. Drylie on 19 Apr 2000, 11:40 p.m.,
in response to message #1 by Eric

Dear Eric; I'm no friend to the hp 48 series, but I'll explain what I know. First of all, you have a manual in your 48. Type the word TEACH into the command line and press enter. This loads the examples directory from built in memory into your Home directory where you can access it. Press VAR and softkey EXAM to open examples directory. Then go to PLOTS and LISSA. LISSA is a parametric plot program of the Lissajou figure. When you press LISSA it will plot this for you. When finished, you can access the parametric plot form and you can see how the equation was entered in parametric form. Now, two things to keep in mind. First you must be able to rewrite the two parametric functions x(t) y(t) into a complex-valued function f(t)=x(t)+ iy(t) and sometimes this is not easy. Example, The figure called the Lemniscate of Bernouilli is written thusly; x=a x COS theta x SQRT of COS 2 x theta. y=a x SIN theta x SQRT of COS 2 x theta. Now, written for the hp 48 is 'COS x (pi/4 x T) x SQRT of COS (2xpi/4xT) + i x SIN (pi/4xT) x SQRT of COS (2xpi/4xT)'. Notice the i which puts the eqation in complex form and the T is a parameter for the 48, it must also be factored in. For the Lemniscate, set your parameters to H-view -1.5 1.5 and V-view -.8 .8 Radians mode and Independant T. Enjoy the figure. The second thing to keep in mind is keep your angle mode straight. When working with trig functions, be in radians mode. If not, 98% of the time the 48 will not graph anything. I hope this helps you. Cheers Bill

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