Quirky simplification (TI-92)
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Quirky simplification (TI-92)
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My TI-92 refused to cooperate in simplifying an expression today in my
Differential Equations class, and I was wondering if anyone out there has
had a similar experience, and/or knows why it did this.
Without going into all the details, I wanted to confirm that
y(x) = (x/2 + 3/4) e^(x)
was a solution to
y'' - 5y' + 6y = x * e^(x)
So I typed in
(x/2 + 3/4)*e^(x) -> y(x)
d(d(y(x),x),x) - 5 d(y(x),x) + 6y(x)
which resulted in the output
-5(2x+5)e^x 3(2x+3)e^x / x \
----------- + ---------- + ( - + 3/4 ) e^x + e^x
4 2 \ 2 /
I was surprised that it didn't come out simpler than this, but I typed in
Expand(ans(1))
expecting to see it result in "x e^x" ... but it simply returned exactly the
same (unsimplified) expression!
A student with a TI-92+ was able to get the correct simplification (and
confirm that this y(x) really was a solution to the DE), but I finally had
to move on. After class I experimented some more and discovered that
Factor(ans(1))
and
tExpand(ans(1))
both work (that is, they result in the simplified answer).
Can anyone reproduce (or explain) this?
--
Darryl K. Nester E-mail: mailto:nesterd@bluffton.edu
Assoc. Prof. of Mathematics WWW: http://www.bluffton.edu/~nesterd
Bluffton College Phone: 419-358-3483
Bluffton, OH 45817-1704 Fax: 419-358-3232
--
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