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Desmos SAT Math Guide: 8 Calculator Tricks That Save Points

The Digital SAT lets you use the built in Desmos graphing calculator on every math question. Most students never learn what it can actually do. These 8 tricks turn whole problem types into free points.

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The one rule before any trick

Desmos cannot read the problem. It can only graph an equation you give it. So the workflow on every SAT question is the same: read the problem, write the equation yourself, then let Desmos do the solving. The students who struggle are not slow at math, they skip the setup step. Every example below shows both.

1. Solve any equation by graphing both sides

Example

Solve 2x+35=7\tfrac{2x + 3}{5} = 7 for xx.
  1. 1Type the left side as y1: y = (2x + 3)/5
  2. 2Type the right side as y2: y = 7
  3. 3Click the intersection point on the graph.
x=16x = 16

One-variable equations become two lines. The intersection is the answer, no algebra required.

2. Systems of two equations: read the answer straight off the graph

Example

If the system below has the solution (x,y)(x, y), what is x+yx + y?
  1. 1Graph each equation as written, with the variables flipped to y = form if needed.
  2. 2Find the intersection point.
  3. 3Add the two coordinates.
3x+2y=12,x−y=1  ⇒  (2.8,0.8),  x+y=3.63x + 2y = 12,\quad x - y = 1 \;\Rightarrow\; (2.8, 0.8),\; x + y = 3.6

The SAT loves asking for x + y, x - y, or xy. Desmos hands you the coordinates, then it is one quick calculation.

3. Roots, vertex, and number of solutions in seconds

Example

How many real solutions does x2−6x+9=0x^2 - 6x + 9 = 0 have, and where is its vertex?
  1. 1Graph y = x^2 - 6x + 9.
  2. 2Count the x-intercepts: that is the number of real solutions.
  3. 3Click the lowest point to read the vertex.
One solution (the parabola touches at x=3x = 3), vertex (3,0)(3, 0)

Discriminant questions are instant here. Two intercepts means two real roots, one means exactly one, none means the answer is zero real roots.

4. Line of best fit with one click

Example

A table shows hours studied and test scores for 10 students. Which equation best models the data?
  1. 1Click the plus icon, choose Table, and type the pairs in.
  2. 2In the next row type y1 ~ m x1 + b (the tilde tells Desmos to fit a line).
  3. 3Desmos shows the slope m and intercept b right on screen.
y≈6.2x+41y \approx 6.2x + 41

Regression questions look scary but they are free points. The ~ symbol works for quadratic fits too: y1 ~ a x1^2 + b x1 + c.

5. Inequalities: let the shading pick the answer

Example

Which point satisfies the system y>2x−1y > 2x - 1 and y≤−x+4y \leq -x + 4?
  1. 1Type both inequalities exactly as written.
  2. 2Desmos shades the solution region.
  3. 3Test the answer choices: type the point as a coordinate to see if it lands in the shaded area.
(1,3)(1, 3) works: 3>13 > 1 and 3≤33 \leq 3

You can also type the whole answer choice list into a table and see which points sit inside the shading.

6. Absolute value equations without cases

Example

What are all values of xx where ∣2x−4∣=10|2x - 4| = 10?
  1. 1Graph y = abs(2x - 4) and y = 10.
  2. 2Click the two intersection points.
x=−3x = -3 and x=7x = 7

No splitting into positive and negative cases, no sign mistakes. Desmos uses abs( ) for absolute value.

7. Growth and decay: match the equation visually

Example

A population of 500 grows 8% per year. After how many years is it closest to 800?
  1. 1Graph y = 500(1.08)^x.
  2. 2Graph y = 800.
  3. 3Click the intersection and read the x value.
x≈6.7x \approx 6.7, so about 7 years

Any percent-growth or decay model becomes one exponential line plus one horizontal line.

8. Desmos cannot read the problem. Translate first, then graph.

Example

A gym charges a 50signupfeeplus50 sign up fee plus30 per month. After how many months does the total reach $260?
  1. 1Turn the words into an equation first: 50 + 30m = 260.
  2. 2Graph y = 50 + 30x and y = 260, then find the intersection.
m=7m = 7 months

This is the habit that separates 600s from 700s: the calculator is only as good as the equation you feed it. Set up first, graph second.

Common questions

Is Desmos allowed on the Digital SAT?

Yes. The Bluebook test app includes a built in Desmos graphing calculator that you can use on every math question, both modules. There is no separate calculator section anymore.

Is the Desmos calculator on the SAT the same as the website?

It is the full Desmos graphing calculator, not the scientific one. If you know the website version at desmos.com/calculator, you already know the test version.

Should I use Desmos for every question?

No. Easy arithmetic and one step algebra are faster by hand. Desmos is at its best on systems, quadratics, inequalities, regressions, and any equation with a variable on both sides.

How do I practice Desmos before the test?

Use the free calculator at desmos.com/calculator and run the drills in this guide. In Bluebook practice tests, open the calculator icon and use the real test version at least once before test day.

More free resources

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