Texas Instruments TI-89 Tip List page 426

For loop slower on the TI-92 than the TI-8x products - why?
The For..EndFor loop on the TI-92 uses its arguments to compute the remaining step count every time
thru the loop. This provides great flexibility. If variables are used to specify the step size and end value,
then these variables, along with the index variable, can be altered within the body of the loop, thus
affecting how the loop operates.
The TI-8x products did not do this. They allow the index value to be altered within the body of the loop,
but the end value and the step value are computed only once when the loop is started.
I only have 70K bytes for user memory - why?
The TI-92 system has a lot of integrated software and it needs memory (RAM) to allow all the features
to work correctly.
Gamma Function
Define gamma(n)=integrate(x^(n-1)*e^(-x),x,0,infinity)
gamma(5) returns 24. If n is an integer, gamma(n) returns (n-1)!
Implicit differentiation
Why does d(x^2 + y^2, x) return 2x, not -2x/(2y)? What is happening is that since you are taking the
derivative with respect to x, y is viewed as a constant. A constant squared is still a constant and the
derivative is zero, hence the answer.
Here is a first derivative implicit differentiating function based on a more general function found in
DERIVE.
define impdif (uu, xx, yy)=-d(uu,xx)/d(uu,yy)
where uu is an expression that equals 0, and d() is the derivative function. The variables xx and yy
are used to avoid a circular definition error that will occur when you differentiate a function of x and y.
Then, enter, for example:
impdif(x^2+y^2,x,y)
-x/y is returned, which is the reduced form of -2x/(2y)
How "complete" is the TI-92's symbolic manipulation?
The symbolic manipulation features set was designed with teachers around the country to address the
needs of Algebra I, Algebra II, Trig, Pre-Calculus, and Calculus courses.
Geometry figure on TI-92 manual - how to create it.
To create the locus on the manual follow these steps:
! Go to the geometry editor.
! Draw a segment. (F2, 6)
! Put a point on the line a couple of centimeters from the left end point. (F2, 2)
! Create a perpendicular line through the line segment at this point. (F4, 1)
! Draw a circle with the center on the perpendicular line and the radius point being the intersection
point of the segment and perpendicular line. (F3, 1)
! Measure the distance from the left endpoint to the intersection point of the circle and the segment.
(F6, 1)
B - 15