# Angle Lock in the Geometry Tool?

Is there a way to lock angles in the geometry tool? Similar to how you can lock points? In the example below, I want to lock the 90 degree angle so that if I pull on the two purple points, they only go outwards in a line. This would be useful in exploring different congruence conditions for triangles (something I’m doing in a Desmos CL Lesson). Students would be able to more easily construct triangles that meet specific angle and side measure criteria, and then see that other students either created the exact same triangle, or created something different.

https://www.desmos.com/geometry/sjfwtfdyzc

Here’s one method: https://www.desmos.com/geometry/8lergezgow. I created a line, then in the “Transformations” menu picked one of the points to be the center for a rotation. Selecting the line and applying the transformation gave me a new line with a 90 degree angle; I placed a new point on this line and did a bit of clean up with styling and hidden objects!

You could also potentially recreate the experience in the graphing calculator. If you have access to Desmos’ curriculum, there is a lesson on similar triangles that sounds very similar to what you are describing!