#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.
#20
(a) AB//DC [ adjacent angles are supplementary ]
(b) PS//QR [ ditto ]
#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.
