ACT Math study guide · Chapter 43
Using Desmos and Your Calculator
The current online National ACT includes a built-in Desmos graphing calculator inside the Math section's tools menu; an approved handheld calculator is permitted on both the online and paper formats. Format facts, timing, and the calculator policy itself were already stated in full in “How ACT Math Is Organized” near the start of this book and are not repeated here. This section is about the interface, not the policy.
Desmos opens to a blank graphing screen with an entry line for typed expressions, equations, or coordinate points, and a settings icon controls the viewing window. A table mode accepts a list of x-values and generates corresponding y-values for a given function, useful for checking several inputs at once instead of evaluating one at a time by hand. The ACT's embedded Desmos tool does not include a dedicated matrix mode; matrix arithmetic is instead a job for a familiar approved handheld calculator with matrix functions, or for hand calculation. Students coming from a different graphing tool should spend a few minutes with the actual ACT online practice environment beforehand, since keystrokes and menu locations are not identical across platforms.
Every content chapter in this book already named where Desmos genuinely helps and where it doesn't, next to the specific mathematics it applies to: evaluating complex arithmetic in Part I, sidestepping the extraneous-root mistake on a radical equation in Part I, checking a system's intersection in Part II, confirming a function's zeros or end behavior in Part III, reading a circle's center or a conic's vertex in Part IV, and computing a regression line in Part V. That pattern is not repeated in full here. The table below is only a compact index back to it.
| Content area | What Desmos is good for | What it cannot decide |
|---|---|---|
| Complex numbers, radicals (Part I) | Evaluating arithmetic; graphing both sides of a radical equation to sidestep the extraneous-root check | Whether a number is rational or irrational |
| Vectors (Part I) | Plotting points and checking a magnitude calculation numerically | Matrix arithmetic; the ACT's embedded Desmos has no dedicated matrix mode, so matrices are a handheld or hand job |
| Systems, quadratics (Part II) | Finding an intersection point directly; graphing a parabola's roots and vertex | Which algebraic method is fastest for a given equation |
| Functions (Part III) | Evaluating, composing, and checking transformations numerically | What a function's domain restriction should be |
| Geometry, conics (Part IV) | Graphing a circle or conic to confirm a center or vertex | Which theorem or geometric relationship applies |
| Statistics (Part V) | Computing mean, median, standard deviation, and a regression line from entered data | Whether a study design supports a causal conclusion |
A calculator, handheld or Desmos, is a tool that removes work. If a specific route requires more menu navigation, re-entry, or window adjustment than the mathematics itself would take by hand, that route has stopped doing its job for that particular question, regardless of which tool it is.