07-29-2018, 01:11 PM
Post: #1
 ettlz Junior Member Posts: 20 Joined: Aug 2014
Prime 2.0.0.13865 gives a bizarre form of the derivative of sin(sin(x)): I get (1/2)*cos(sin(x)+x) + (1/2)*cos(-sin(x)+x). OK it's correct but I'd expect cos(sin(x))*cos(x) (straightforward chain rule). Getting to that form doesn't work with simplify() and I've not played around with the other trig-rewrite functions.
07-29-2018, 01:13 PM (This post was last modified: 07-29-2018 01:16 PM by Tim Wessman.)
Post: #2
 Tim Wessman Senior Member Posts: 2,293 Joined: Dec 2013
I am guessing you have simplified to "maximum"? "Maximum" is equivalent to just tapping the "simplify" button on each result.

I'd highly recommend not doing that if you are and leave the default "minimum" - it has a tendency to mess things up and we will probably remove that option completely at some point before too much longer.

TW

Although I work for HP, the views and opinions I post here are my own.
07-29-2018, 01:18 PM (This post was last modified: 07-29-2018 01:25 PM by ettlz.)
Post: #3
 ettlz Junior Member Posts: 20 Joined: Aug 2014
Ah yes. It seems cos(x)*cos(sin(x)) is one of those cases where simplify() makes things more complicated.

Going the other way, the HP 50g's SIMPLIFY does get from the long form back to cos(x)*sin(cos(x)), so there's a sort-of "regression" here. (Well, assuming the Prime represents a functional continuation... which probably isn't entirely fair!)
07-29-2018, 01:38 PM
Post: #4
 parisse Senior Member Posts: 1,322 Joined: Dec 2013
It's not "more complicated", it's different, the product of cosines has been replaced by a sum. There is no way to magically "simplify" because there is no simpler form.
07-29-2018, 02:21 PM
Post: #5
 Aries Member Posts: 159 Joined: Oct 2014
(07-29-2018 01:11 PM)ettlz Wrote:  Prime 2.0.0.13865 gives a bizarre form of the derivative of sin(sin(x)): I get (1/2)*cos(sin(x)+x) + (1/2)*cos(-sin(x)+x). OK it's correct but I'd expect cos(sin(x))*cos(x) (straightforward chain rule). Getting to that form doesn't work with simplify() and I've not played around with the other trig-rewrite functions.

immagini su internet

Best,

Aries
07-29-2018, 03:57 PM
Post: #6
 Tim Wessman Senior Member Posts: 2,293 Joined: Dec 2013
Yes, which is exactly what Prime gives in it's default state.

TW

Although I work for HP, the views and opinions I post here are my own.
07-29-2018, 04:06 PM
Post: #7
 Komanguy Junior Member Posts: 49 Joined: Jul 2018
(07-29-2018 02:21 PM)Aries Wrote:
(07-29-2018 01:11 PM)ettlz Wrote:  Prime 2.0.0.13865 gives a bizarre form of the derivative of sin(sin(x)): I get (1/2)*cos(sin(x)+x) + (1/2)*cos(-sin(x)+x). OK it's correct but I'd expect cos(sin(x))*cos(x) (straightforward chain rule). Getting to that form doesn't work with simplify() and I've not played around with the other trig-rewrite functions.

immagini su internet

Best,

Aries

Hp prime gives the same result.

Guy R. KOMAN, hp 50G, hp Prime Rev. C
07-29-2018, 04:12 PM (This post was last modified: 07-29-2018 04:23 PM by Komanguy.)
Post: #8
 Komanguy Junior Member Posts: 49 Joined: Jul 2018
(07-29-2018 03:57 PM)Tim Wessman Wrote:  Yes, which is exactly what Prime gives in it's default state.

diff(sin(sin(x))) always gives : cos(x)*cos(sin(x)) independently of the simplification mode in cas settings!

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Guy R. KOMAN, hp 50G, hp Prime Rev. C
07-29-2018, 04:19 PM
Post: #9
 DrD Senior Member Posts: 1,133 Joined: Feb 2014
(07-29-2018 04:12 PM)Komanguy Wrote:  diff(sin(sin(x))) always gives : cos(x)*cos(sin(x)) independently of the simplification mode in cas settings!

Now try it on the physical prime!
07-29-2018, 04:25 PM
Post: #10
 Komanguy Junior Member Posts: 49 Joined: Jul 2018
(07-29-2018 04:19 PM)DrD Wrote:
(07-29-2018 04:12 PM)Komanguy Wrote:  diff(sin(sin(x))) always gives : cos(x)*cos(sin(x)) independently of the simplification mode in cas settings!

Now try it on the physical prime!

I have the physical one. I donâ€™t use the emulator.

Attached File(s) Thumbnail(s)

Guy R. KOMAN, hp 50G, hp Prime Rev. C
07-29-2018, 05:43 PM (This post was last modified: 07-29-2018 05:45 PM by DrD.)
Post: #11
 DrD Senior Member Posts: 1,133 Joined: Feb 2014