Two adjacent sides of the rectangle ABCD have the length AB = 7, BC = 3. From point D there is drawn a straight line that intersects side AB at point E, and then a straight line perpendicular to line DE that passes through point E and intersects side BC at point F ( see the picture on the right). Know that DE = 3EF, find the area of the quadrilateral DEFC.

We consider parallelograms with a circumference of 16 cm and an acute angle of 45.

Find the lengths of the sides of the parallelogram whose area is equalT