I would like to be able to see the result of a "Trace" or "Calc" operation in a fraction form when on the "Graph" screen of a TI-84 Plus. I assume that this is either a simple fix or it is not possible.
The specific math problem: Find y at x = -5 for the equation y = sqrt([x^2]-4).
Note: I specifically want to solve these types of questions on a graphing calculator, not algebraically. I know how to solve it by graphing the function and then using the "Trace" function to find y for x = -5, but the result is 4.5825757 and I want the result displayed in a fraction form.
Best Answer
While I believe you can plug in inputs of fractions, or decimals, or any form you want with the Ti-84, a Ti-84 does not have the necessary technology to actually compute fractions, except with some simple cases.
With your example, the result would be $y=\sqrt{21}\approx 4.583$. Since $\sqrt{21}$ is irrational it is not expressible as a fraction with integer parts, so it wouldn't even be expressible as a fraction regardless of the technology you had.
If you do want to find exact forms, you will need a more powerful piece of technology. This can be done with a device that has a computer algebra system (abbreviated as CAS) e.g. the Ti-Nspire CX CAS. An even more powerful software is wolfram alpha, which can give possible closed forms for numbers from even the decimal expression. For example, if you scroll down in this Wolfram Alpha link, you will find $\sqrt{21}$.