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24-Ruby IV
Nov 22, 2014 4:23 AM UTC
Question

sin(x)/x solve,x

I would like to show my students a symbol math in Mathcad and in Internet. But:

sym-mp-math.png

6 replies

Werner_E
25-Diamond I
Nov 22, 2014 10:05 AM UTC

Its well known that Mathcad's symbolics unfortunately is very weak and in no way state of the art.

Here it misses the fact that your function is undefined for x=0. It gets even worse, if you tell Mathcad to omit x=0:

0.png

Its beyond my understanding why we get -72*pi now and why MuPad switches to float mode.

The symbolics seem sto consider the nominator only in these cases and finds a wrong "solution", similar as in the following:

2.png

BTW, WolframAlpha's result could be simplified to

1.png

so its not perfect, either, but at least the result given is correct.

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19-Tanzanite
Nov 22, 2014 1:52 PM UTC

How about:

sincroots.PNG

(sinc(x) is Mathcad's built in function for sin(x)/x; though, if you prefer, you could replace it with sin(x)/x in the above and would get the same results)

Alan

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24-Ruby IV
Nov 22, 2014 5:20 PM UTC

Thanks, but

sinc.png

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19-Tanzanite
Nov 23, 2014 8:54 AM UTC

Yes, that's why I gave the solution in two separate ranges.

For some reason Mathcad insists on giving x=0 as a solution if the range crosses from negative to positive. I suspect it is actually just solving sin(x) = 0.

Alan

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24-Ruby IV
Nov 25, 2014 4:58 AM UTC

One Buridan's ass problem

https://en.wikipedia.org/wiki/Buridan%27s_ass

y(x):=sin(x)/x x:=0 root(y(x), x)= ???

I think we use the Newton method in Prime (???=error)

http://communities.ptc.com/videos/1411

and the secant method in Mathcad 15 (???=1910 pi)

http://communities.ptc.com/videos/1466

PS

*** not from me but from PlanetPTC

ass.png

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