Prof. Keely's Math Online Lessons
University of Phoenix Online & Clark College, Vancouver WA
Copyright © 2000 Sally J. Keely. All Rights Reserved.

CALCULATOR GUIDE

To find an x-Intercept Point using ZERO or ROOT:

To find an x-intercept point of a graph on a TI-84:

With the equation already graphed, press the 2ND CALC menu then ZERO.

It asks, "Left bound?". Move the cursor using your left/right scroll buttons to just left of an x-intercept point and press ENTER. It asks, "Right bound?" Move the cursor to just right of that x-intercept point and press ENTER. It asks, "Guess?". Move the cursor near that x-intercept point and press ENTER. (See diagram below.)

It should then give you the x-intercept point x=#, y=0 :)

If there is another x-intercept point to find, repeat these steps.
To find an x-intercept point of a graph on a TI-86:

With the equation already graphed, press MORE MATH ROOT (that is the "math" on the screen, not the hard key).

It asks, "Left bound?". Move the cursor using your left/right scroll buttons to just left of an x-intercept point and press ENTER. It asks, "Right bound?" Move the cursor to just right of that x-intercept point and press ENTER. It asks, "Guess?". Move the cursor near that x-intercept point and press ENTER. (See diagram below.)

It should then give you the x-intercept point x=#, y=0 :)

If there is another x-intercept point to find, press EXIT to get the graph menu back and repeat the steps above.
To find an x-intercept point of a graph on a TI-89:

With the equation already graphed, press F5 (the MATH menu) then ZERO.

It asks, "Lower bound?". Move the cursor using your left/right scroll buttons to just left of an x-intercept point and press ENTER. It asks, "Upper bound?" Move the cursor to just right of that x-intercept point and press ENTER. (See diagram below.)

It should then give you the x-intercept point x=#, y=0 :)

If there is another x-intercept point to find, repeat these steps.

Example 1. Find the x-intercept point of y = 7.4 - 2.8x accurate to the nearest thousandth.

Graph the equation. You should get a line with a negative slope. Use ZERO or ROOT to find the x-intercept point. The answer is (2.643,0).

Sometimes the calculator gives the y-value of the x-intercept point as "1E-13". This is scientific notation meaning 1x10-13=0.0000000000001, pretty darn close to zero. Treat "1E-13" as zero.

Example 2. Solve x2 - 2.8x = 5.33 accurate to the nearest tenth by graphing.

Always start by moving everything to one side of the equation so it is set equal to zero:  x2-2.8x-5.33=0. Graph y1=x2-2.8x-5.33. Did you get a parabola (a U-shape) that has two x-intercept points like the one shown at the right? Good!

The solutions to the equation are the x-coordinates of the x-intercept points. Use ZERO or ROOT to find the x-intercept points. The final answers to the equation are x = -1.3, 4.1.

As a visual check, make sure that those x-intercept values match where the graph crosses the x-axis.

Originally written: 2000-05-08
Last revision: 2009-01-30 05:22 PM

Copyright © 2000 Sally J. Keely
All Rights Reserved.
www.InteGreat.ca/MOL

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