TI-84 Geometric Sum Program (ACT/SAT Calculator Hack!)

Learn how to program your TI-84 calculator to find the sum of a geometric series — a powerful sequence shortcut for ACT and SAT math!
This tutorial guides you through creating a TI-84 program that asks for the first term, the common ratio, and the number of terms, then uses the geometric sum formula:

Sₙ = a(1 - rⁿ) / (1 - r)

If you want faster problem solving, higher confidence, and less test anxiety, these calculator programs will help you master the math section.

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I’m Tina Wiles, test anxiety expert and founder of My2tor & ACTSATPrepHQ.com.
I help students master the mindset, strategy, and content they need to succeed on high-stakes exams like the ACT and SAT.

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⏱ Timestamps
00:00 Intro
00:14 Geometric sequence review
00:36 Creating new program (GEOSUM)
00:58 Prompt for first term (A)
01:15 Prompt for ratio (R)
02:22 Prompt for number of terms (N)
02:32 Writing geometric sum formula
03:04 Storing result
03:20 Displaying the sum
03:33 Running and testing the program
03:40 Example: a=2, r=3, n=3 → 26
04:06 Outro

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