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24-Ruby IV
November 22, 2014
Question

sin(x)/x solve,x

  • November 22, 2014
  • 3 replies
  • 2628 views

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

sym-mp-math.png

3 replies

25-Diamond I
November 22, 2014

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.

19-Tanzanite
November 22, 2014

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

24-Ruby IV
November 22, 2014

Thanks, but

sinc.png

19-Tanzanite
November 23, 2014

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

24-Ruby IV
November 25, 2014

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