Solve the question first when you know the method. Use Desmos to confirm the number, not to hunt for a method you have not learned. What the tool includes is in Desmos on the ACT.
Check, then move
If you factored and got x = 4, graph the quadratic and see whether it crosses the axis at 4. If you solved a system and got (2, 5), type both equations and look for that intersection. A mismatch means redo the arithmetic, not start a new approach from the graph unless you are stuck.
Fraction choices should be checked in fraction form, which is in fraction answers in Desmos.
When checking is the slow path
A one-step percent or a comparison you can see should stay on paper or in your head. That cutoff is in when not to use Desmos. The same idea for a handheld calculator is in when not to use your calculator.
The bottom line
Get an answer, then let the graph agree or disagree. Do not open Desmos as a substitute for recognizing the question.
Start practicing
Start with a free diagnostic, then drill your weak spots with 15-question quizzes and track how you're doing across Reading, English, and Math. Compare plans whenever you're ready to go further.
This article offers general ACT prep guidance. The ACT can change from year to year, including its format, scoring, policies, test dates, and fees, so always confirm the latest details on the official ACT website at act.org before you make decisions. ACT® is a registered trademark of ACT, Inc. thirty-six is not affiliated with, endorsed by, or sponsored by ACT.