Construct a line perpendicular to CB.[br]1. Use the Circle with Centre through Point tool to draw circles centered at B and C with radii BC.[br]2. Using the Intersect tool, mark where these 2 circles intersect.[br]3. Use the Line tool to draw a line segment between these points of intersection.[br]4. Use the Intersect tool to mark where this new line intersects BC.[br]5. Use the Distance or Length tool to measure the distance between the point of intersection to point B and again to point C.[br]6. Use the Angle tool to measure the size of the angle at this point of intersection. Click point B, then the point of intersection on segment BC, and then the topmost point of your constructed line segment.