Weegy: AB CD and AD is a transversal; Therefore, A + D = 180°;
Similarly, B + C = 180°, C + D = 180° and A + B = 180°; For example, A, B are adjacent angles and A = 90°, [ then:
A + B = 180°;
90° + B = 180°;
B = 180° – 90°;
B = 90°;
Similarly, C = D = 90°. ]
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