How to Solve SAT Linear Equations with Desmos
Last updated: September 28, 2026
Type the left side of the equation on one row, the right side on the next, then click where the two lines cross. The x-coordinate of that point is your answer. Two rows and one click — no rearranging, no moving terms across the equals sign.
The problem
Solve: 3x − 4 = x + 2
Solution: x = 3
What do you type?
Open the calculator from the toolbar in the math module, then type two things.
- Row 1: 3x − 4
- Row 2: x + 2
You do not type "y =" in front of either one. Desmos reads a bare expression in x as a function and draws it. You also do not rearrange the equation first — whatever sits left of the equals sign goes on row 1, whatever sits right of it goes on row 2, exactly as the question printed them.
Press Enter after the first row to get the second. Two straight lines appear.
How do you read the answer off the screen?
Find the point where the lines cross and click it. Desmos labels it (3, 5).
The x-coordinate is the answer: x = 3.
The y-coordinate is a free check. It is what both sides come out to when x = 3 — 3(3) − 4 = 5, and 3 + 2 = 5. If the height of the crossing matches what you get putting your answer back into the equation, you typed the right thing. If you fat-fingered a coefficient, those two numbers will not agree.
Don't read the answer off the gridlines. A crossing that looks like it sits on x = 3 might be at 2.98, and on a grid-in that costs you the point. Click the point and let Desmos say the number.
What if the lines don't seem to cross?
Almost always it is the window, not the equation. The crossing is off screen. Zoom out until you can see both lines and the angle between them, then zoom back in on the crossing before you click it.
If you zoom out and the lines stay parallel, or one sits exactly on top of the other, that is a real answer rather than a typing mistake. SAT Linear Equations in One Variable covers what each of those two cases means.
When is typing it in slower than solving it?
When the keystrokes cost more than the algebra does. 3x − 4 = x + 2 takes a few seconds by hand, and this post uses it because it is short enough to show the whole method at once.
Graphing pays off on the ones that would take real work: decimals, fractions, parentheses on both sides, the variable showing up in three places. Those are the same two rows to type no matter how ugly they get, and Desmos does not make arithmetic slips.
Practice one keystroke before test day. Typing / opens a fraction, and everything you type after it lands in the denominator until you press the right arrow key to get back out. It catches people the first time they hit it. Type a few fractions now, not in module 2.
How do you practice this?
Take 10 linear equations you can already solve on paper. Solve each one by hand, then graph both sides and check the crossing against your answer.
You are after two things. The keystrokes should stop needing thought. And you should find out what the method actually costs you — time yourself across all 10, because that number is what tells you on test day whether to graph an equation or just solve it.
HIROSCORE tracks your accuracy on linear equations as its own skill, separately from the rest of Algebra, so you can see whether graphing is helping you or eating your clock. The GPS for your SAT score.
Ready to practise Linear Equations in One Variable?