Axial symmetry - reflection in a line
Try yo work out where the image of the triangle will be first before you reveal the answer. Move point D or E to move the line. Move a, B or C to change the shape of the triangle.
You can use the "polygon tool" to draw a triangle where you think the reflection will be. Click "Show Reflection" to check your drawing. Use refresh to return to the start. Drag the points to move the triangle and the line and try different variations.