The Desmos Advantage: 4 "Cheat Codes"
The built-in calculator on the Digital SAT is not just for arithmetic. It is a powerful graphing engine that can solve 60% of "Hard" algebra questions for you. Here is exactly how to use it.
Trick 1: Systems of Equations
The Algebra Way
Question: 5x - 3y = 12 AND y = 2x - 5
1. Isolate variable...
2. Substitute (2x-5) into top equation...
3. Distribute negative signs...
4. Solve for x, then plug back in for y.
Time: 2 Minutes. Risk: High (Sign errors).
The Desmos Way
Strategy: Type them exactly as written. The answer is literally where the lines cross.
Time: 15 Seconds. Risk: Zero.
Trick 2: The "Magic Tilde" (Regression)
If the SAT gives you a table of points and asks for an equation, never calculate slope manually. Use the Regression feature.
The Secret Symbol: ~
In Desmos, using ~ instead of = tells the calculator: "Find the best fit line for these points."
PARAMETERS:
m = 2
b = 1
Result: Desmos tells you m=2 and b=1. The equation is y = 2x + 1.
Trick 3: Using Sliders for Constants
Question Type: "The graph of y = ax² + c passes through (2, 10). What is a possible value for c?"
Instead of doing algebra, just type the equation with letters. Desmos will ask "add slider?". Click "Yes" and drag the slider until the line hits the point.
Trick 4: Instant Function Evaluation
Question Type: "If g(x) = 3x² - 4x + 5 , what is the value of g(-3) ?"
Don't risk a negative sign error by doing mental math. Define the function once, then let Desmos calculate the values.
Why this wins
On the SAT, you might need to calculate g(2), g(0), and g(-5) all for one problem. Once you type line 1, you can just change the number in line 2 instantly.