ĐỀ THAM KHẢO KIỂM TRA 1 TIẾT CHƯƠNG III – HÌNH HỌC 9

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 Từ một điểm A ở ngoài đường tròn (O) kẻ hai tiếp tuyến AB, AC đến (O) (B; C là hai tiếp điểm).

Gọi H là giao điểm của OA và BC, qua H kẻ một đường thẳng vuông góc với OB cắt (O) tại D (D thuộc cung nhỏ BC). AD cắt (O) tại E (E khác D). Gọi K là trung điểm của DE.

a)      Chứng minh : 5 điểm A, B, O, K, C cùng nằm trên một đường tròn.

b)      Chứng minh : tứ giác KCDH nội tiếp.

c)      Chứng minh : AH. AO = AD. AE và tam giác OKH là tam giác cân.

d)     Kẻ OI vuông góc với CE tại I. Chứng minh ba điểm I, K, H thẳng hàng.

 



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