Texas Instruments TI-82 Getting Started page 19

Technology Tip: As you zoom in, you may also wish to change the spacing between tick marks on the axis
so that the viewing window shows scale marks near the intercept point. Then the accuracy of your
approximation will be such that the error is less than the distance between two tick marks. Change the scale
on the TI-82 from the WINDOW menu. Move the cursor down to Xscl and enter an appropriate value.
The x- intercept of a function's graph is a root of the equation
CALCULATE menu (Figure I.45) and choose 2 [root] to find a root of this function. Set a lower bound,
upper bound, and guess as described in Section I.2.8. The TI-82 shows the coordinates of the point and
indicates that it is a root (Figure I.57).
TRACE and ZOOM are especially important for locating the intersection points of two graphs, say the
3
graphs of y x 4x
intersection point. Then press
change, but the y- coordinate is likely to be different (see Figures I.58 and I.59).
When the two coordinates are as close as they can get, you have come as close as you now can to the point y-
of intersection. so zoom in around the intersection point, then trace again until the two
close as possible. Continue this process until you have located the point of intersection with as much accu-
racy as necessary. The points of intersection are approximately
−4.7
−3.2
Figure I.58: Trace on
You can also find the point of intersection of two graphs by pressing 2nd CALC 5 [intersect]. Trace with
the cursor first along one graph near the intersection and press ENTER; then trace with the cursor along the
other graph and press ENTER. Marks
near the point of intersection and press ENTER again. Coordinates of the intersection will be displayed at
the bottom of the window. More will said about the intersect feature in Section I.3.3.
Technology Guide
Graphing
−10
Figure I.57: A root of
and y .25x. Trace along one of the graphs until you arrive close to an
or to jump to the other graph. Notice that the
3.2
4.7
3
y x 4x
are placed on the graphs at these points. Finally, move the cursor
Copyright © by Houghton Mifflin Company. All rights reserved.
So press 2nd CALC to display the
f x 0.
10
10
−10
3
y x 8x
2.062, 0.515 ,
−4.7
Figure I.59: Trace on
x-
x-
x- coordinate does not
y- coordinates are as
0, 0 , and 2.062, 0.515 .
3.2
4.7
−3.2
y .25x
I-19