Circumscribing a triangle is a method of finding a circle that passes through the three vertices in the triangle. To do this we must find the circumcenter of the triangle, which is also the intersection of the triangle’s perpendicular bisectors.

1. Create a point to start the triangle.

2. Draw one of the triangle sides by dragging from the point with the Line tool selected.

3. Draw lines from the new point to create the rest of the triangle.

4. Now we need to construct the perpendicular bisectors. You could do this the traditional way with the compass tool, but there is also a convenient shortcut in Isosceles. First tap and hold on one of the lines. Then tap Info in the pop-up that appears. You should see a menu like this:

5. Tap Perpendicular Bisector to draw the perpendicular bisector. Then repeat for the other sides of the triangle.

6. For this step, make sure you have Shows Intersections turned on in the Canvas section of Settings. The circumcenter is the intersection of the perpendicular bisectors, so simply tap on the intersection with the default pencil to create it. If the perpendicular bisectors are too short to intersect, you can use the Points tool to move the triangle’s vertices so that they do intersect.

7. To construct the circumcircle, select the Circle tool and drag from the circumcenter (point D) to one of the vertices. As you move the vertices with the Points tool, the circumcenter and circumcircle will move in real-time with the triangle.

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When I draw a circle and then draw a point on the circle, the point will snap to the circle easily enough, but later when I try to drag the point around the circle, the point won’t stay on the circle. How do I make it so that once I draw a point on a circle, I can drag it around without it coming off the circle? Also, how I re-size a circle after I’ve drawn it?

Points you drag near enough to a circle will automatically show a green highlight and snap to the circle when you lift your finger.

To make a circle with changeable radius, tap out two points and then connect them using the Circle tool. When you drag the points, the circle will automatically adjust its radius.

Thanks for using Isosceles!

Is there a way to change the fill opacity? Also, it would be easier to set colors if it could be done by changing the RGB values. The isometric geometry system is pretty cool.

Not as of yet, but these features are on my agenda for future updates of Isosceles. Glad you like the isometric system!