∠XAS = ∠Y CV since ∠DAB = ∠XAS and ∠BCD = ∠Y CV both subtend the
same arc of the circle, and ∠ASX = ∠CV Y since both are right angles, so 4ASX ∼
∠CV Y by the A-A similarity criterion. It follows in particular that |XS|
|Y V |
=
|AX|
|CY |
both subtend the same arc of the circle
.