Desmos Tricks

Poly-Solve Variables

Solve for k when you know x.

⚡ The "Variables to y" Trick

The Golden Rule: Desmos loves x and y. It gets a bit confused by other letters like k, m, or a.

💡 Pro Tip: If you see a mystery variable like \(k\), simply call it \(y\) instead. This lets Desmos see it as a line so you can find the answer!

4x + 2y = 18

x = 3

📝 SAT Problem

If \(4x + 2k = 18\) and \(x = 3\), what is the value of \(k\)?

(A) 2
(B) 3
(C) 4.5
(D) 6

Step 1: FORCE 'y' into the equation

You CANNOT type 4x + 2k. It won't work because Desmos only wants to use x and y.

You MUST type 4x + 2y = 18.

Step 2: Type the known value

Type x = 3 on the next line.

Step 3: Click the Dot

Find the intersection point. The y-coordinate is your answer.

Desmos Poly Solve Solution

The intersection is at (3, 3). Since we swapped k for y, this means:

y = 3   ➝   k = 3

✅ Final Answer:

3 (Choice B)