1/28+1/70+1/130+1/208+...+1/3190
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Những câu hỏi liên quan
1/4+1/28+1/70+1/130+1/208
Hãy giúp mình với
\(\frac{1}{4}+\frac{1}{28}+\frac{1}{70}+\frac{1}{130}+\frac{1}{208}\)
\(=\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+\frac{1}{10.13}+\frac{1}{13.16}\)
\(=\frac{1}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}\right)\)
\(=\frac{1}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}\right)\)
\(=\frac{1}{3}.\left(1-\frac{1}{16}\right)\)
\(=\frac{1}{3}.\frac{15}{16}=\frac{5}{16}\)
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1/1.4+1/4.7+1/7.10+..+1/13.16
1-1/4+1/4-1/7+..+1/13-1/16
1-1/16
15/16
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1/2 +1/4 + 1/28 +1/70 +1/130 + 1/208
Tinh tong tren
=13/16
cách của mình ngắn gọn hơn cơ
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1/4+25/28+67/70+127/130+205/208+301/303
1/4+1/28+1/70+1/130+1/208 dang gi vay mn lam thanh bai giai ho minh nha
\(\frac{1}{4}+\frac{1}{28}+\frac{1}{70}+\frac{1}{130}+\frac{1}{208}\)
\(=\frac{1}{1\times4}+\frac{1}{4\times7}+\frac{1}{7\times10}+\frac{1}{10\times13}+\frac{1}{13\times16}\)
\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}\)
\(=1-\frac{1}{16}=\frac{15}{16}\)
Chúc bạn học tốt ^^
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Bài 1: Tính nhanh;
A = 6/4 + 6/28 + 6/70 + 6/130 + 6/208
1/2A=1/2(6/4+6/28+6/70+6/130+6/208)
= 3/4+3/28+3/70+3/130+3/208
= 1-1/4+1/4-1/7+..................-1/16
=1-1/16
=15/16 => A=15/8
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a, X-3/4-3/28-3/70-3/130-3/208= 1/6
b, (1/15+1/35+1/63)xX =1
C, 242/363+1616/2121=2/7xX
A 2/1x3 + 2/3x5 + 2/5x7 +...+ 2/ 21x23
B1/6 + 1/12 +1/20 +1/30+1/42+1/56+1/72+1/90
C1/28+1/70 +1/130+1/208
mng ơi giúp tớ vs aa tớ đg cần rất gấp, tớ cảm ơn mng trước ạ!!!
hnay tớ phải nộp rùi , giúp tớ vs aa(
Đọc tiếp
A = 2/1x3 + 2/3x5 + 2/5x7 +...+ 2/ 21x23
B=1/6 + 1/12 +1/20 +1/30+1/42+1/56+1/72+1/90
C=1/28+1/70 +1/130+1/208
mng ơi giúp tớ vs aa tớ đg cần rất gấp, tớ cảm ơn mng trước ạ!!!
hnay tớ phải nộp rùi , giúp tớ vs aa=(
\(A=\dfrac{2}{1x3}+\dfrac{2}{3x5}+\dfrac{2}{5x7}+...+\dfrac{2}{21x23}\)
\(A=2x\left(\dfrac{1}{1x3}+\dfrac{1}{3x5}+\dfrac{1}{5x7}+...+\dfrac{1}{21x23}\right)\)
\(A=2x\dfrac{1}{2}x\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{21}-\dfrac{1}{23}\right)\)
\(A=1-\dfrac{1}{23}\)
\(A=\dfrac{22}{23}\)
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\(B=\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{72}+\dfrac{1}{90}\)
\(B=\dfrac{1}{2x3}+\dfrac{1}{3x4}+\dfrac{1}{4x5}+\dfrac{1}{5x6}+\dfrac{1}{6x7}+\dfrac{1}{7x8}+\dfrac{1}{8x9}+\dfrac{1}{9x10}\)
\(B=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\)
\(B=\dfrac{1}{2}-\dfrac{1}{10}\)
\(B=\dfrac{5}{10}-\dfrac{1}{10}\)
\(B=\dfrac{4}{10}\)
\(B=\dfrac{2}{5}\)
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\(C=\dfrac{1}{28}+\dfrac{1}{70}+\dfrac{1}{130}+\dfrac{1}{208}\)
\(C=\dfrac{1}{4x7}+\dfrac{1}{7x10}+\dfrac{1}{10x13}+\dfrac{1}{13x16}\)
\(C=\dfrac{1}{3}x\left(\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{16}\right)\)
\(C=\dfrac{1}{3}x\left(\dfrac{1}{4}-\dfrac{1}{16}\right)\)
\(C=\dfrac{1}{3}x\left(\dfrac{4}{16}-\dfrac{1}{16}\right)\)
\(C=\dfrac{1}{3}x\dfrac{3}{16}\)
\(C=\dfrac{1}{16}\)
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M=1/4+1/28+1/70+1/130+...+1/9700
\(3M=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{97.100}\)
\(3M=\frac{4-1}{1.4}+\frac{7-4}{4.7}+...+\frac{100-97}{97.100}\)
\(3M=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{100}\)
\(3M=1-\frac{1}{100}\)
\(3M=\frac{99}{100}\)
\(M=\frac{33}{100}\)
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Tính tổng : M = 1/4 + 1/28 + 1/70 + 1/130 + ... + 1/8008
M=1/4+1/4.7+1/7.10+1/10.13+.............+1/88.91
3M=3/4+3/4.7+3/7.10+3/10.13+........+3/88.91
3M= 3/4+1/4-1/7+1/7-1/10+1/10-1/13+......+1/88-1/91
3M=3/4+1/4-1/91=1-1/91=90/91
----->M= 30/91
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