#17 Use property that the diagonals of a parallelogram bisect each other, => x+y=18 y+(can't read)=22 Solve for x and y.
#18 z+60=180 [angles on a line are supplementary] x=z [opposite angles of a parallelogram are congruent] y=50 [alternate interior angles between parallel lines AD and BC]
#19 3v=30 [ opposite sides of a parallelogram are congruent ] solve for v. 2u-1=19 [ ditto ] solve for u.
#21 1) a parallelogram with one angle 90 means the adjacent angles are 180-90=90. This in turn means all angles are 90, so the figure is a rectangle (adjacent sides may or may not be equal in a parallelogram). 2) a rectangle with adjacent sides equal must be a square.
