Answer:
Given:
In Rhombus QRST, diagonals QS and RT intersect at W and U∈QR and point V∈RT  such that UV⊥QR. (shown in below diagram) 
To prove: QW•UR =WT•UV
Proof:
In a rhombus diagonals bisect perpendicularly,
Thus, in QRST
QW≅WS, WR ≅ WT and m∠QWR=m∠QWT=m∠RWS=m∠TWS=90°.
In triangles QWR and UVR,
 (Right angles)
              (Right angles)
 (Common angles)
              (Common angles)
By AA similarity postulate,

The corresponding sides in similar triangles are in same proportion,


 (∵ WR ≅ WT )
                 (∵ WR ≅ WT )
Hence, proved.