Explanation:
15. x = 148°, z = 32°
In a parallelogram, adjacent angles are supplementary, so must add to 180°. That also means opposite angles are congruent.
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17. x = 8, y = -3
The diagonals bisect each other, so ...
2x -4 = 12
x = (12 +4)/2 = 8
and ...
y +10 = 7
y = 7 -10 = -3
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21. The diagonals of a parallelogram bisect each other, so their point of intersection is their midpoint. The midpoint of WY can be computed as ...
P = (W+Y)/2 = ((-3, 5) +(3, 1))/2 = (0, 6)/2 = (0, 3)
The diagonals intersect at (0, 3).
