Solution 11944: Correcting the Error "NO SIGN CHANGE" When Calculating the Zero (Root) of a Function Using the TI-83 Family, TI-84 Plus Family or TI-Nspire™ Handheld in TI-84 Plus Mode.
Why am I getting the error "NO SIGN CHANGE" when using the zero function on a TI-83 family, TI-84 Plus family and TI-Nspire handheld in TI-84 Plus mode?
When using the TI-83 family, TI-84 Plus family and TI-Nspire handheld in TI-84 Plus mode, finding the zero of a function requires entering a "left bound", "right bound" and a "guess". These requirements can be entered by inputting a specific value or by using the arrow keys to scroll and select a value on the graph. Pressing [ENTER] after each value will mark the left bound, right bound and guess.
After entering the left and right bounds, select as the guess a point that is between the two bounds and as near as possible to the zero of the function. Selecting the upper bound as the guess will return, for some functions, the "NO SIGN CHANGE" error message. The calculator will also get the "NO SIGN CHANGE" error message when calculating a zero of a function that does not cross the x axis for example: y=x^2.
To resolve the this, try zooming in as close as possible to the location of the zero while still being able to separate the function from the axis line. To zoom in, please do the following:
1) Press [ZOOM] .
2) Scroll as close as possible to the zero of the function.
3) Press [ENTER].
4) Repeat as neccesary.