Point P is the perpendicular to BC and CD, and the vertical feet are E and F respectively.

PE = PQ

∠BPE=∠QPF

∠PEB=∠PFQ

∴△PBE≌△PQF？

PB=PQ

2.S quadrilateral BPQC=S square EPFC

PC= root number 2-x?

y=PE^2=PC^2/2=？ (root number 2-x? )^2/2