ABCD is a quadrilateral. AB is parallel with DC, and angle A + angle B = 180°. Prove that ABCD is a parallelogram?

[匿名]

2016-07-03 12:11 pm

更新1:

@戇戇居士 Thank you.

回答 (1)

戇戇居士

2016-07-03 12:19 pm

✔ 最佳答案

∠DAB + ∠ABC = 180° (given)
Hence, DA // BC (int. ∠s. supplementary)

AB // DC (given)

ABCD is a parallelogram (two pairs of opp. sides //)

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