Kẻ Ot // Ax // By
Ta có: Ot // Ax
=> góc A + góc O1 = 1800 (TCP)
hay 1400 + góc O1 = 1800
=> góc O1 = 1800 - 1400 = 400.
Ta có: Ot // By
=> góc A + góc O2 = 1800 (TCP)
hay 1100 + góc O2 = 1800
=> góc O2 = 1800 - 1100 = 700
Ta có: góc AOB = góc O1 + góc O2
= 700 + 400 = 1100,
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