TI-84 ERR:NO SIGN CHNG — What It Means & Fix

What Does This Error Mean?

TI-84 ERR:NO SIGN CHNG means the root-finding algorithm looked for where a function crosses zero between your two bounds but did not find a sign change. Either there is no root in the interval, or both bounds are on the same side of the x-axis. Zoom out on the graph to find where the function crosses zero, then set tighter bounds around that crossing.

Affected Models

TI-84 Plus
TI-84 Plus Silver Edition
TI-84 Plus CE
TI-84 Plus CE-T
TI-83 Plus

Common Causes

The function does not cross zero in the interval defined by the left and right bounds
Both left and right bounds are on the same side of the x-axis (both positive or both negative)
The root is a tangency — function touches zero without crossing (even multiplicity)
Incorrect equation entered — the function as entered has no real roots
The Solver's guess value is far from the actual root

How to Fix It

Graph the function and visually identify where it crosses zero.

Press Y= and enter your equation. Press ZOOM → 6: ZStandard to see the default window. Look for where the graph crosses the x-axis. If no crossing is visible, press ZOOM → 3: Zoom Out several times to expand the view.
Set left and right bounds that straddle the crossing.

In the graphing Zero finder (2nd → CALC → 2: Zero), after pressing Left Bound, move the cursor to the LEFT of the x-intercept and press ENTER. Then move to the RIGHT of the intercept for Right Bound. The function value must be negative on one side and positive on the other.
In the Equation Solver, set the guess near the expected root.

Press MATH → 0: Solver. Enter the equation (set equal to zero) and set the initial guess to a value close to the expected root. Narrow the lower and upper bounds to a small interval that you know contains the root.
Check whether the function touches but does not cross zero.

Some equations touch the x-axis without crossing (e.g. y = x²). The TI-84 root-finder requires a sign change to locate a root. For a tangency, use CALC → Minimum or Maximum instead of Zero.
Verify the equation was entered correctly.

A common mistake is entering Y1 = X² + 4 when the intention was X² - 4. Press Y= and verify every term, especially negative signs and exponents. A small entry error can result in an equation that has no real roots.

Frequently Asked Questions

What does 'sign change' mean in the context of ERR:NO SIGN CHNG?

A sign change means the function value goes from positive to negative (or vice versa) as x passes through the root. For example, if Y(-2) = -3 and Y(1) = 5, there must be a root between x = -2 and x = 1. ERR:NO SIGN CHNG means no such crossing was found in the specified interval.

Can I find complex roots using the TI-84 root-finder?

No. The TI-84 root-finder only finds real roots. For complex roots, use the quadratic formula manually or use the polynomial root-finder in the POLY submenu (MATH → 0 → scroll).