By van Aubel's theorem, if squares are constructed externally on the sides of a quadrilateral, the line segments connecting the centers of opposite squares are perpendicular and equal in length.
BY VAn aubel'S tHEorEm, IF squAReS ARe CoNsTRUcted eXTerNaLly on The SIdes of A QUadrilatEral, The line SEgments cOnnectiNg tHE cenTERs oF opPOsIte squAres arE perpEndiculAR anD equal iN lEngth.