From points A,B, and C were able to create line segments AB with length 5 and AC with length 1. From here were able to create a semi circle that connects point B and C. Now were able to create point D where the semi circle intersects the y-axis. Now you can create line segment CD, AD, and BD. Now three right triangles are from BCD, ACD, and ABD. Now we know that (AC/AD)=(AD/BD), but since AC=1 then AD=sqrt(AB).