Open the dynamic geometry application by [APPS] 8:Geometry and give a name to your new construction.

Draw a circle filling most of the screen. Press [F3] 1:Circle , move the cursor to the middle of the screen, press [ENTER], move the cursor to the top edge of the screen, press [ENTER].

Mark in the diameter, noting that it must pass through the centre of the circle. One way to do this is [F2] 4:Line, move cursor to the midpoint of the circle until you get the confirmation thru this point, press [ENTER] and [ENTER] again when you have moved the line to appear horizontal. Now press [F3] 3:IntersectionPoint, move the cursor to one end of the diameter until you get the confirmation point at this intersection, press [ENTER] and repeat the process to mark a point at the other end of the diameter

Now delete the original line. Move the cursor to any place on the line until you see this line. Press [F7] 1:Hide/Show and press [ENTER]. The line should go dotted. Press [ESC] and the line disappears, leaving the two points on the circumference which are guaranteed to be the endpoints of the diameter.

To draw the triangle, press [F3] 3:Triangle, move the cursor to one of the diameter endpoints on the circumference (until you see this vertex point), press [ENTER], move the cursor to the other diameter endpoint on the circumference (until you see thru this vertex), press [ENTER], and finally move the cursor to any other point on the circumference (until you see on this circle) and press [ENTER]. The triangle in the semicircle has now been constructed.

We now need to measure the angles. Press [F6] 3:Angle. In general, to measure angle ABC you must point the cursor and press [ENTER] at points A, B, and C in that order. (Ensure you get the confirmation message this point before pressing ENTER.) Repeat this procedure to measure all three angles of the triangle.

The angle measurements appear at fairly arbitrary position on the screen. To reposition them, press [F1] 1:Pointer, move the cursor over the number, hold down the [BLUE HAND] and drag the number to a more suitable position.

Dynamically change the triangle by moving the cursor over the point on the circumference, hold down the [BLUE HAND] and drag the point. Note that the point is constrained to lie on the circumference. The angle measurements change automatically.

Drag the point on the circumference a small distance to produce each of the frames for the animation.

Use the TI-GRAPHLINK to capture each screenshot, copy each image into a graphics software package to save as a .gif file, and use these individual images with your chosen GIF Animation programme.