Một người đàn ông muốn chèo thuyền ở vị trí A tới...
Câu hỏi: Một người đàn ông muốn chèo thuyền ở vị trí A tới điểm B về phía hạ lưu bờ đối diện, càng nhanh càng tốt, trên một bờ sông thẳng rộng 3km (như hình vẽ). Anh có thể chèo thuyền của mình trực tiếp qua sông để đến C và sau đó chạy đến B, hay có thể chèo thuyền trực tiếp đến B, hoặc anh ta có thể chèo thuyền đến một điểm D giữa C và B và sau đó chạy đến B. Biết anh ấy có thể chèo thuyển 6km/h, chạy 8km/h và quãng đường BC = 8km. Biết tốc độ dòng nước là không đáng kể so với tốc độ chèo thuyền của người đàn ông. Tìm khoảng thời gian ngắn nhất (đơn vị: giờ) để người đàn ông đến B.![](data:image/png;base64,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)
A \(\dfrac{{\sqrt {73} }}{6}.\)
B \(1 + \dfrac{{\sqrt 7 }}{8}.\)
C \(\dfrac{3}{2}.\)
D \(\dfrac{9}{{\sqrt 7 }}.\)
Câu hỏi trên thuộc đề trắc nghiệm
Đề thi thử THPT QG môn Toán trường THPT Lương Văn Tụy - Ninh Bình - lần 1 - năm 2018 (có lời giải chi tiết)