Toán Lớp 7: Tính nhanh tổng sau: F=$\frac{1}{1.1985}$ +$\frac{1}{2.1986}$ +$\frac{1}{3.1987}$ +…+$\frac{1}{16.2000}$
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Toán Lớp 7: Tính nhanh tổng sau: F=$\frac{1}{1.1985}$ +$\frac{1}{2.1986}$ +$\frac{1}{3.1987}$ +…+$\frac{1}{16.2000}$
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1984F=(1.1984/1.1985+1.1984/2.1986+1.1984/3.1987+…+1.1984/16.2000)
1984F=(1984/1.1985+1984/2.1986+1984/3.1987+…+1984/16.2000)
1984F=(1-1/1985+1/2-1/1986+…+1/16-1/2000)
F=1/1984.[(1-1/2+…+1/16)-(1/1985+1/1986+…+1/2000)]