Pythagorean Theorem – TI-84 Evo Math Program

Type the two sides of a right triangle you know and this program gives you the third, whether that's the hypotenuse or a missing leg.

By CalcPlex.

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Press the prgm key. The PROGRAMMING menu opens.
Press enter to select TI-Basic. The list of TI-Basic programs opens.
Press enter on PYTHAG in the program list, which puts prgmPYTHAG on the home screen.
Press enter to run it. The program opens with a menu asking which side of the triangle you're missing.

Press enter to choose Hypotenuse. The program asks for the two legs, one at a time. Type each leg and press enter after it. For legs of 3 and 4, the moment you enter the second one it answers Hypotenuse=5.

Run the program again. A single enter on the home screen reruns it, and the menu comes back.
Scroll down to A leg and press enter. Now it asks for the leg you know, then the hypotenuse. With a leg of 5 and a hypotenuse of 13, it fills in Other leg=12.

It's the Pythagorean theorem, worked out for you. The program solves a² + b² = c² for whichever side you asked about: √(a² + b²) for the hypotenuse, √(c² − a²) for a leg.
Sides don't have to be whole numbers. Decimals work at every prompt: legs of 1.5 and 2 give Hypotenuse=2.5.
Answers that aren't whole come out as decimals. Legs of 2 and 4 give 4.472135955 rather than the exact √20. If you want the tidy radical form, the Radical Simplifier program turns 20 into 2√5.
Rerun it with one keypress. Pressing enter on the home screen repeats whatever you ran last, so right after a run, a single enter brings the menu straight back.
The hypotenuse is always the longest side. In the A leg option, if the leg you type is as long as the hypotenuse or longer, the program answers "Hypotenuse must be longest" instead of dropping you on an error screen.