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From: edp@jareth.enet.dec.com (Eric Postpischil (Always mount a scratch monkey.))
Newsgroups: comp.sys.handhelds
Subject: Re: A strange feature (a bug?)
Keywords: symbolic integration/differentation in DEG mode
Message-ID: <15930@shlump.nac.dec.com>
Date: 10 Oct 90 12:44:46 GMT
References: <1990Oct10.093506.8848@wuarchive.wustl.edu>
Sender: newsdaemon@shlump.nac.dec.com
Reply-To: edp@jareth.enet.dec.com (Eric Postpischil (Always mount a scratch monkey.))
Organization: Digital Equipment Corporation
Lines: 22

In article <1990Oct10.093506.8848@wuarchive.wustl.edu>,
hp48sx@wuarchive.wustl.edu (HP48SX Archive Maintainer) writes:

>If I try to evaluate dX(sin(X)) then I get:
>cos(x)*(dX(X)*(pi/180))
>/* if the factor pi/180 should be applied, then it should be multiplied
>   to the x in cox(x), but even this is not correct */
>further EVAL gives:
>cos(X)*(pi/180)
>
>And we all know that cos(60) is 1/2  (the 60 is in degrees), and this is
>the correct result. But we still get the factor (pi/180) which will give
>me a wrong result.

I think the result given is correct.  If you plot sin(X) where X is measured in
degrees, the slope of that plot at X = 60 degrees will be pi/360.

The derivative of sin(x) is cos(x) only if x is in radians.  If the argument is
in degrees, then the derivative of sin(x) is cos(x)*(pi/180).


				-- edp