# Correctness of a Circle

I know how to check a function that a student enters for correctness by comparing it the correct answer. I am, however, struggling to think of a way to check the equation of a circle for correctness. Example: I want the student to write the equation of a circle that has a center of (2, 3) and a radius of 4. Therefore, I want “(x-2)^2 + (y+3)^2 = 16” to display a checkmark on the dashboard.

This might help you out. It samples points so maybe not 100% reliable, but pretty close. Circle Checker • Activity Builder by Desmos

1 Like

Awesome!! I would have never thought about a function with 2 variables! Thank you so much!

I watched the webinars to see if it had anything for circles and I heard you mention creating something to check a circle, I just didn’t know how to find it. Thanks again!

Is there anyway to make the circle they enter in the input box display on the graph too?

here is how I did it. circle example • Activity Builder by Desmos

Awesome!!! A combination of these two gets me exactly what I was looking for. Thanks so much!

I want to copy this because it is EXACTLY what I need. However, desmos won’t let me. Can you share your CL please?

I would love to, but it uses rawExpression which no long is supported.

This is what I used. rawExpression(“f”): Input5.latex
I looked quick to see if I could figure something out, but I am out of time before my classes start today.

Hopefully somebody knows a workaround for this, because I would like to know too!

Sorry I can’t help more.

Ok thank you so much!

updated here: Circle Checker â¢ Activity Builder by Desmos