Desmos Knowledge - Your SAT Math Superpower

A key piece of advice I emphasize to my students is to get used to the Desmos functions and tools before test day. There are so many things Desmos can do, and not all of them are relevant during the SAT. Having an understanding of what each tool does, and a game plan for which ones you will use and when, is crucial.

Where can I find Desmos during the test? 

Desmos can be found by clicking the “Calculator” button on the upper right hand corner during the test. 

This will pop up a smaller window with Desmos.

When is Desmos helpful? 

Desmos is often helpful for questions involving: 

  • Functions

  • Systems of equations

  • Inequalities

  • Visualizing graphs or relationships 

  • Equations with constants 

    • Note: These can be tricky! Have a plan of attack for each type of constant question before test day – some constant problems are easier to solve algebraically than by graphing.

When should Desmos not be used? 

Desmos isn’t as helpful for questions with: 

  • Answer choices with fractions and/or radicals

  • “Student-produced” responses with equations 

  • Complicated, abstract equations in the answer choices 

Students will also not need to use advanced Desmos tools such as:

  • Derivatives or Calculus

  • Advanced statistics

  • Geometry functions

Examples using Desmos

Inequalities

Example Question:

y> 12x-4

y -3x +6

Which of the following is a solution to the system of inequalities above? 

  1. A) (-1, -3)

  2. B) (5,0)

  3. C) (3, -5)

  4. D) (4, -3)

Desmos is helpful for solving inequality questions because it automatically shades in the solutions for each equation. Below, I graphed the two inequalities as well as the answer choices as coordinate points. 

For a point to be a solution, it must fall in the overlap of both equations’ shaded regions. After inputting the answer choices as coordinate points, we can see that only Choice A is located in that region. 

Using sliders 

Example Question: 

y= -3x2+bx-2

In the given equation, b is a positive integer. The equation has two solutions. What is the lowest possible value of b

  1. 0

  2. 1

  3. 4

  4. 5

For this question, we can test the answer choices with the slider function. After inputting the equation into Desmos, click “add slider”.

With all the fancy tools of Desmos, can I stop studying for the math section? 

No! You still need solid foundational knowledge to succeed on the math section of the SAT. Think of Desmos as your cool side kick. It can help you get from point A to B, but it cannot do the work for you. There are still so many trap answers to look out for while using Desmos! 

Example: 

y= 5x+7

y= -4x-2

If the ordered pair (x, y) is the solution to the systems of equations above, what is the value of x

Using Desmos, we get the following graph. I marked the solution of the equations as well as other commonly used trap answers. Can you identify the true answer and trap answers? 

To solve, we look for the point where the two lines intersect. From the graph, the lines intersect at (-1, 2), so the value of x is -1.

Trap answers often come from the x– or y-intercepts, but those aren’t the solution to the system. Desmos helps visualize, but understanding what to look for is key!

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