The diagonals of a parallelogram ABCD intersect ay O. If BOC =90° and BDC=50°, then OAB =

BOC is 90°

So,


COD and AOB all should be 90° by linear pair


BDC is 50°,


So,


Now as in a parallelogram the opposite sides are equal


We say,


AB parallel to CD


DCA = 50°


So,


In triangle COA


C = 50° (Stated above)


COA = 90° (Proved above)


Therefore,


90° + 50° + x° = 180°


x = 40°

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