weLearnUsing Desmos on Digital SAT Math: what it’s good for
The calculator rules for the Digital SAT, and the Desmos moves worth learning before test day: intersections, zeros, vertices, sliders, tables and regression.
On the Digital SAT you can use a calculator for the whole Math section, and Bluebook has one built in: Desmos, with a graphing mode and a scientific mode you can switch between. You may bring your own approved calculator instead (no computer-algebra models, no stored programs with algebra functions), but most students end up using Desmos because it is already on the screen.
No calculator is allowed in Reading and Writing.
Why it matters
Desmos turns many algebra questions into “draw it and look”. That is faster and safer for some questions, and slower for others. The skill is knowing which is which, and you only get that by practising with it.
Moves worth learning
Solve an equation by graphing both sides. For something like 2x + 7 = 5x − 8, type y = 2x + 7 and y = 5x − 8 on separate lines and click where the lines cross. The x-coordinate is the answer.
Solve a system of equations. Type both equations as they are. The intersection point is the solution. If the lines are parallel, there is no solution; if they lie on top of each other, there are infinitely many.
Zeros, vertex, maximum and minimum. Type a quadratic such as y = x^2 − 6x + 5. Desmos marks the x-intercepts and the vertex; click them to read the coordinates.
Sliders for unknown constants. If a question says “for what value of k does the equation have no solution?”, type the equation with k and let Desmos create a slider. Drag it and watch what changes.
Tables and regression. Put data in a table (x₁, y₁ columns), then fit a line by typing y₁ ~ m x₁ + b. Useful for “line of best fit” questions.
Check answer choices. When the options are equations or points, graph them and see which one matches the conditions.
When not to use it
- Simple arithmetic you can do in your head.
- Questions that are really about reading a word problem correctly. Graphing the wrong equation quickly is still wrong.
- Anything where typing takes longer than thinking.
How to practise
College Board suggests getting comfortable with the embedded Desmos through the Bluebook test preview, a Bluebook practice test, or the Desmos website. Do a few Math sets where you decide consciously for each question: by hand, or in Desmos? After a week it becomes automatic.