Bluebook, the app you take the SAT in, has the Desmos calculator built in for the entire Math section. It can switch between a graphing and a scientific view. Used well, it turns some long algebra problems into a few seconds of typing. Used for everything, it slows you down.
The rules in one paragraph
A calculator is allowed on every Math question. You can use the built-in Desmos calculator or bring your own approved handheld calculator. Calculators with computer algebra systems (CAS) are not allowed, and you can’t use a calculator during Reading and Writing. Always check College Board’s current calculator policy before test day.
Where Desmos saves real time
- Systems of equations. Type each equation on its own line and click the intersection. The point is the solution.
- “How many solutions?” Graph each side of the equation as its own function and count where they cross.
- Vertex, maximum and minimum. Graph the quadratic and click the turning point.
- Zeros and x-intercepts. Click where the graph meets the x-axis.
- Unknown constants. Type the equation with the constant, say k, accept the slider Desmos offers, and drag until the condition in the question is true.
- Tables of data. Enter the data in a table and fit a line or curve to find a model.
- Checking work. Plug an answer choice back in, or graph your solution, before moving on.
When to skip it
If a question takes one line of arithmetic or a fact you already know, solve it by hand. Simple percent questions, many geometry questions and anything that asks what a number in a model represents are usually faster without a graph. Desmos is a tool, not a rule.
Habits that prevent careless errors
- Parentheses everywhere. Wrap fractions and exponents: type
(1/2)^(t/5), not1/2^t/5. - Re-read what is asked. Desmos may show you the intersection when the question wants only the y-value, or the sum of the coordinates.
- Zoom to fit. If the important part of a graph is off screen, zoom out instead of guessing.
- Clear old work. Delete earlier expressions between questions so old graphs don’t mislead you.
- Mind the variable names. Desmos graphs in x and y. Rewrite t or n as x when you graph.
How to practise
Desmos is free online, so practise with the same tool you will use on test day. A good drill: for the next twenty Math questions you do, solve each one twice, once by hand and once in Desmos, and note which was faster. Within a couple of weeks you will recognise in seconds which approach fits a question. Full-length practice tests in Bluebook let you use the exact built-in version.