Let KLMN be a trapezoid (see added picture). From the point M put down the trapezoid height MP, then quadrilateral KLMP is square and KP=MP=10. A triangle MPN is right and <span>isosceles, because </span>m∠N=45^{0}, m∠P=90^{0}, so m∠M=180^{0}-45^{0}-90^{0}=45^{0}.Then PN=MP=10. The ttapezoid side KN consists of two parts KP and PN, each of them is equal to 10, then KN=20 units. Area of KLMN is egual to sq. units.