Question 310458
Solution:

LBAC= LBCD( opposite angles of a parallelogram are equal)
.
LBAC + LBCD = 180° ( opp. angles of a cyclic quadrilateral are  supplementary)
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LBAC=LBCD= 90°
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Similarly LABC=LADC=90°
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ABCD is a rectangle ( all the angles are =90°)

L stands for angle