The locus of P such that angle APB is always 90o is a circle with the midpoint of AB as the centre and with radius equals to half the length of AB, excluding the points A and B. Click on the animation button to trace the locus. To erase the trace, click on the button [X] at the bottom.
Note: JavaSketchpad cannot support shading of the angle APB. To see this, open the file IT4EMLociAngle90.gsp using Geometer's Sketchpad. If you cannot see the JavaSketch below, click here to troubleshoot.