[TI-M] Can TI-89 do this math?


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[TI-M] Can TI-89 do this math?




Hi:

I'm considering buying a TI-89 to have a calculator that can better 
assist me at times when I can't remember some things like trig 
identities and basic integral tables.  I have TI-83, but that is a lot 
of trouble to use to verify identities, and I have to be pretty sure of 
then to start with.

But I am doubtful about the TI-89's symbolic math abilities.  I went to 
a store and tried to do a one-sided Laplace transform of some simple 
functions, which it failed to evaluate.  Then it occurred to me after I 
left that maybe it could have done it in two parts.

I tried:

integrate( e^(s*t)*t,t,0,infinity )

which returned "undef" or maybe infinity, I forget.  And I tried:

integrate( e^(s*t)*sin(t),t,0,infinity )

An astute reader will recognize that I made an error in that the Laplace 
transform should have a minus sign in the exponent of e.  However, this 
has little effect on the outcome, as the result returned from the first 
integral should look something like:

1/s^2 if Re(s)>0, else undef

and so the case of a positive exponent would simply cause the condition 
to be if Re(s)<0.

Can the TI-89 accept assumptions that would make it return a result in 
this case?

Another approach would be to evaluate the definite integral such as

integrate( e^(s*t)*sin(t),t,0,x )

then take the limit as x->infinity.  But this still needs the assumption 
that Re[s]>0.

Can TI-89 take assumptions in either the integral or limit operations?

Any other methods to evaluate this integral or ones like it?


-- 
_____________________
Christopher R. Carlen
crobc@earthlink.net
Suse 7.3 Linux 2.4.10