Cho a,b > 0 chứng minh rằng : \(\frac{1}{a}\) + \(\frac{1}{b}\) ≥ \(\frac{4}{a+b}\)

Cho ΔABC nhọn (AB < AC) có hai đường cao BD và CE cắt nhau tại H.

a) Chứng minh: ΔABD ∼ ΔACE

b) Chứng minh: HD.HB = HE.HC

c) AH cắt BC tại F. Kẻ FI vuông góc AC tại I. Chứng minh \(\frac{IF}{IC}\) = \(\frac{FA}{FC}\)

d) Trên tia đối tia AF lấy điểm N sao cho AN = AF. Gọi M là trung điểm cạnh IC. Chứng minh: NI ⊥ FM

P/s: Giải nhanh cho mình đi ạ, mình đang cần gấp. Không cần phải vẽ hình đâu ạ!

1. He said: "I have cleaned my house."

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2. Nina said: "My dog has eaten everything."

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3. She said to me: "I have given this book to you."

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4. She said: "I have work here for three years."

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5. Nina said: "I have been sick for five days."

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6. He said to her: "I have washed your dishes."

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7. My mother said to me: "You have finished eating."

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8. He said: "I have seen this movie."

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9. Tom said: "I have studied this lesson since last week."

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10. He said: "I have eaten snake meat."

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1. He said: "I lived in VietNam last year."

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2. Nina said to me: "You were busy yesterday."

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3. Nina said to me: "You didn't turn off your computer last night."

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4. My mother said to her: "you bought this house."

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5. He said: "I listened tomusic yesterday."

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6. I said to them: "you painted your house red."

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7. She said: "I repaired this car."

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8. Tom said: "I was handsome."

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9. My sister said: "It worked well."

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10. He said: "yesterday was cold."

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