partial fractions and complex roots in 50g

• 10-16-2008, 03:46 PM
unix
partial fractions and complex roots in 50g
Hello,

Doing partial fractions with this in the denominator: s^2+10s+169
gives me a crazy result. When I simply factor this, I know why. I get
something involving e^i*ATAN(12/5) etc. All I really want is (s+5-12i)
(s+5+12j).
I played with most of the simplification functions in the ALG and
EXP&LN menus, but none really makes a difference.
I know it's not too hard to do by hand, but that's not why I have this
calculator.

Ultimately I want to get the partial fractions with an expression like
that in the denominator, which I then take the inverse Laplace
transform of. It works great with real roots, just not with complex
roots.

Any ideas?

Thanks!

Christoph
• 10-16-2008, 04:08 PM
unix
Re: partial fractions and complex roots in 50g
On 16 Okt., 17:46, Christoph Koehler <christoph.koeh...@gmail.com>
wrote:
[color=blue]
> Doing partial fractions with this in the denominator: s^2+10s+169
> gives me a crazy result. When I simply factor this, I know why.[/color]

On my 50g it works like this
Choose MODE CAS and check the flag for Complex, OK

Then type enter x^2+10*x+169 and choose EDIT and FACTO
and you get the result, you want

Regards,
Peter
• 10-16-2008, 05:10 PM
unix
Re: partial fractions and complex roots in 50g
If you try it with RECT (rectangular coordinates) mode and Complex
mode both turned on, I think it will do what you want. Having the
coordinates in Polar or Spherical modes causes some complex
expressions to be displayed in polar form, r*exp(i*theta), instead of
rectangular form, a+bi. I've noticed this mode setting also affects
certain integrals.

-wes

On Oct 16, 6:46*pm, Christoph Koehler <christoph.koeh...@gmail.com>
wrote:[color=blue]
> Hello,
>
> Doing partial fractions with this in the denominator: s^2+10s+169
> gives me a crazy result. When I simply factor this, I know why. I get
> something involving e^i*ATAN(12/5) etc. All I really want is (s+5-12i)
> (s+5+12j).
> I played with most of the simplification functions in the ALG and
> EXP&LN menus, but none really makes a difference.
> I know it's not too hard to do by hand, but that's not why I have this
> calculator.
>
> Ultimately I want to get the partial fractions with an expression like
> that in the denominator, which I then take the inverse Laplace
> transform of. It works great with real roots, just not with complex
> roots.
>
> Any ideas?
>
> Thanks!
>
> Christoph[/color]

• 10-17-2008, 03:21 AM
unix
Re: partial fractions and complex roots in 50g
On Oct 16, 12:10*pm, Wes <wjltemp...@yahoo.com> wrote:[color=blue]
> If you try it with RECT (rectangular coordinates) mode and Complex
> mode both turned on, I think it will do what you want. *Having the
> coordinates in Polar or Spherical modes causes some complex
> expressions to be displayed in polar form, r*exp(i*theta), instead of
> rectangular form, a+bi. *I've noticed this mode setting also affects
> certain integrals.[/color]

I am so glad you figured that out. That was exactly it, and it makes a
lot of sense.

Thanks again!

Christoph
• 10-18-2008, 01:50 PM
unix
Re: partial fractions and complex roots in 50g
On Thu, 16 Oct 2008 10:10:43 -0700 (PDT), Wes <wjltemp-gg@yahoo.com>
wrote:
[color=blue]
>If you try it with RECT (rectangular coordinates) mode and Complex
>mode both turned on, I think it will do what you want. Having the
>coordinates in Polar or Spherical modes causes some complex
>expressions to be displayed in polar form, r*exp(i*theta), instead of
>rectangular form, a+bi. I've noticed this mode setting also affects
>certain integrals.
>[/color]

Could you please point me to ANY HP50 manual where the above procedure
is described?

A.L.
• 06-08-2009, 12:25 PM