gIẢI TOÁN HÌNH LỚP 7: Cho tam giác ABC có góc A< 90 độ. Vẽ ra phía ngoài tam giác đó hai đoạn thẳng AD vuông góc và bằng AB; AE vuông góc và bằng AC, GỌI h LÀ CHÂN ĐƯỜNG VUÔNG GÓC, Kẻ từ A đến BC. Chứng minh rằng HA đi qua trung điểm của DE

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