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TL:
\(\frac{12}{100}\)= 0,12
\(\frac{5}{100}\)= 0,05
\(\frac{306}{1000}\)= 0,306
-HT-
=13/12x14/13x15/14x16/15x...x2006/2005x2007/2006x2008/2007
=2008/12
=502/3
A = 1\(\dfrac{1}{12}\) \(\times\) 1\(\dfrac{1}{13}\) \(\times\) 1\(\dfrac{1}{14}\) \(\times\) 1\(\dfrac{1}{15}\) \(\times\) ... \(\times\) 1\(\dfrac{1}{2005}\) \(\times\) 1\(\dfrac{1}{2006}\) \(\times\) 1\(\dfrac{1}{2007}\)
A = ( 1 + \(\dfrac{1}{12}\)) \(\times\) ( 1 + \(\dfrac{1}{13}\)) \(\times\) ( 1 + \(\dfrac{1}{14}\)) \(\times\)...\(\times\) ( 1 + \(\dfrac{1}{2006}\))\(\times\)(1+\(\dfrac{1}{2007}\))
A = \(\dfrac{13}{12}\) \(\times\) \(\dfrac{14}{13}\) \(\times\) \(\dfrac{15}{14}\) \(\times\) ...\(\times\) \(\dfrac{2007}{2006}\) \(\times\) \(\dfrac{2008}{2007}\)
A = \(\dfrac{13\times14\times15\times...\times2007}{13\times14\times15\times...\times2007}\) \(\times\) \(\dfrac{2008}{12}\)
A = 1 \(\times\) \(\dfrac{502}{3}\)
A = \(\dfrac{502}{3}\)
Ta có công thức tổng quát:
\(\dfrac{k}{n\cdot\left(n+k\right)}=\dfrac{1}{n}-\dfrac{1}{n+k}\)
\(a,A=\dfrac{1}{5\cdot8}+\dfrac{1}{8\cdot11}+...+\dfrac{1}{x\left(x+3\right)}\\ =\dfrac{1}{3}\left(\dfrac{3}{5\cdot8}+\dfrac{3}{8\cdot11}+...+\dfrac{3}{x\left(x+3\right)}\right)\\ =\dfrac{1}{3}\left(\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11}+...+\dfrac{1}{x}-\dfrac{1}{x+3}\right)\\ =\dfrac{1}{3}\cdot\left(\dfrac{1}{5}-\dfrac{1}{x+3}\right)\\ =\dfrac{1}{3}\cdot\dfrac{x-2}{5\left(x+3\right)}\\ =\dfrac{x-2}{15\left(x+3\right)}\)
Theo đề bài ta có:
\(A=\dfrac{101}{1540}\\ \Rightarrow\dfrac{x-2}{15\left(x+3\right)}=\dfrac{101}{1540}\\ \Rightarrow\dfrac{x-2}{x+3}=\dfrac{303}{308}\\ \Rightarrow\dfrac{x-2}{x+3}=\dfrac{305-2}{305+3}\\ \Rightarrow x=305\)
a; A = \(\dfrac{4026\times2014+4030}{2013\times2016-2011}\)
A = \(\dfrac{2\times\left(2013\times2014+2015\right)}{2013\times2016-2011}\)
A = \(\dfrac{2\times\left(2013\times2016-2013\times2+2015\right)}{2013\times2016-2011}\)
A = \(\dfrac{2\times\left(2013\times2016-4026+2015\right)}{2013\times2016-2011}\)
A = \(\dfrac{2\times\left(2013\times2016-2011\right)}{2013\times2016-2011}\)
A = 2
a) \(\dfrac{2}{3}+\dfrac{3}{5}=\dfrac{10}{15}+\dfrac{9}{15}=\dfrac{19}{15}\)
a) \(\dfrac{7}{12}-\dfrac{2}{7}+\dfrac{1}{12}=\dfrac{2}{3}-\dfrac{2}{7}=\dfrac{14}{21}-\dfrac{6}{21}=\dfrac{8}{21}\)
TL :
a) 8,2
b) 36,23
c) 54,07
d) 12,254
Chúc bn hok tốt ~
Bài 1:
\(2,5=\dfrac{25}{10}=2\dfrac{5}{10}\)
\(4,75=\dfrac{475}{100}=4\dfrac{75}{100}\)
\(2,024=\dfrac{2024}{1000}=2\dfrac{24}{1000}\)
\(75,4=\dfrac{75,4\times10}{10}=\dfrac{754}{10}=\dfrac{750}{10}+\dfrac{4}{10}=75\dfrac{4}{10}\)
\(23,01=\dfrac{23,01\times100}{100}=\dfrac{2301}{100}=23\dfrac{1}{100}\)
Bài 2:
\(57\dfrac{3}{10}=57,3\) Đ
\(25\dfrac{7}{100}=25,7\) S
\(6\dfrac{9}{1000}=6,9\) =>S
19/100=0,19(Đ)
Bài 3:
a: \(6\dfrac{7}{10}=\dfrac{6\times10+7}{10}=\dfrac{67}{10}\)
\(4\dfrac{3}{7}=\dfrac{4\times7+3}{7}=\dfrac{28+3}{7}=\dfrac{31}{7}\)
b:
\(25\dfrac{15}{100}=\dfrac{25\times100+15}{100}=\dfrac{2500+15}{100}=\dfrac{2515}{100}\)
\(47\dfrac{31}{100}=\dfrac{47\times100+31}{100}=\dfrac{4731}{100}\)
Bài 4:
\(1\dfrac{1}{2024}\times1\dfrac{1}{2025}\times1\dfrac{1}{2026}\)
\(=\dfrac{2025}{2024}\times\dfrac{2026}{2025}\times\dfrac{2027}{2026}\)
\(=\dfrac{2027}{2024}\)
1.
2,5 = 2 5/10
75,4 = 75 4/10
4,75 = 4 75/100
3. a. 67/10
b.
2 a. Đ b. S c. S d. Đ
3. a. 67/10
b. 2515/100
c. 31/7
d. 4731/100
4.