Very Very Ergent...

Hello
How can I solve dy/dx=(x^3+y^3)/(x^3-y^3)
Thanks a million...

For implicit differentiation on a 50g, you need to tell it that y is a
function of x (otherwise it assumes that y is a constant). You can do
this by replacing y with Y(X) when entering the expression. Then use
DERVX (like any other derivative) and it gives you something with
d1Y(X) in it. Type in d1Y(X) and use SOLVE (not SOLVEVX because d1Y(X)
is [hopefully] not your system variable). It should return

d1Y(X) = Y(X)/X

In other words, dy/dx = y/x.

Note that in order to type in something like Y(X) you need to use
algebraic mode (i.e. the single quotes). Parenthesis are not valid
syntax in RPN.

S.C.

On my 48GX I just pull up the "Differentiate..." input form in the
"Symbolic" menu, input the above expression, select X (as the variable
of differentiation), make sure "Symbolic" is in the "Result" field,
and press OK.  What comes up is 3*X^2/(X^3-Y^3)-(X^3+Y^3)*(3*X^2)/(X^3-
Y^3)^2.

I think the process is similar on the 49G+ and 50G.

Dick

yamahdiefatemeh:

 > How can I solve dy/dx=(x^3+y^3)/(x^3-y^3)

What is that?  A differential equation?

"Solve this" is easier when one knows what it is ;-)

-=-=-=-

If you mean "urgent", try

'd1Y(X)=(X^3+Y(X)^3)/(X^3-Y(X)^3)'
'Y(X)'
DSOLVE

On the 35s? mwhhha

Mick C

Smells like someone's homework problem to me....

- Kurt

"Very, Very ergent" [sic] smells like someone's TEST problem to me....

How flattering it is that students are Wifi-ing this group during
exams to request answers!


Cheers,
Pal

 XXXX@XXXXX.COM  writes:


If I was looking for a closed form solution, I wouldn't do this on a
calculator.  Anyway, if you substitute y = u*x you can separate the
variables.  You wind up with dx/x on one side and something of the
form f(u)/g(u) du on the other.  All you have to do is integrate both
sides.  g(u) is a quartic.  Find its two quadratic factors and write
f(u)/g(u) as a sum of partial fractions.  Then you can integrate it.
It's a little messy.

Scott
-- 
Scott Hemphill	 XXXX@XXXXX.COM 
"This isn't flying.  This is falling, with style."  -- Buzz Lightyear

In article < XXXX@XXXXX.COM >,



 
In fact, you can do it on an hp49 or hp50.




Even with a calculator to help it is more than a little messy.