Texas Instruments TI-92+, Tip List

Page: 73 / 507

Also, it is possible to create these functions in the Program Editor. Start the editor to create a New
function. In the New dialog box, set the Type to Function and enter a Variable name. Delete the Func
and EndFunc lines. Finally, enter only these lines to define the function:
:sec(x)
: 1 /cos(x)
This will result in a function that can be manipulated by the CAS. You cannot use comments in these
functions.
(Credit to Andy)
[2.15] Use change of variable in limits of when() functions
The CAS may have problems evaluating limits of expressions involving when() functions. For example,
this limit will not be evaluated:
limit(when(x=0, 1 ,sin(x)/x),x,0)
If the limit is expressed as
limit(when(X=k,L,f(X)),X,0)
then substitute x-1 for X to obtain
limit(when(x- 1 =k,L,f(x- 1 )),x, 1 )
The example above becomes
limit(when(x- 1 =0, 1 ,sin(x- 1 )/(x- 1 )),x, 1 )
which returns the correct limit.
(Credit to Martin Daveluy)
[2.16] Find partial fractions with expand()
A proper fraction is the ratio of two polynomials such that the degree of the numerator is less than the
denominator, otherwise the fraction is called improper. Partial fractions is a method to convert an
improper fraction to a sum of proper fractions. While the 89/92+ do not have a specific 'partial fractions'
function, expand() performs that operation, as noted in the 89/92+ manual.
Some examples:
For
x2
+
3x
+
5
x
+
2
use
expand((x^2+3*x+5)/(x+2))
which returns
3
x
+
2
+
x
+
1
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