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a, \(\dfrac{20}{15}=\dfrac{4}{3}\)
b, \(\dfrac{6}{15}=\dfrac{2}{5}\)
c, \(\dfrac{42}{30}=\dfrac{7}{5}\)
d, \(\dfrac{40}{35}=\dfrac{8}{7}\)
e, \(\dfrac{42}{42}=1\)
g, \(\dfrac{54}{10}=\dfrac{27}{5}\)
h, \(\dfrac{12}{15}\)
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1x1=1 6x6=36
2x2=4 7x7=49
3x3=9 8x8=64
4x4= 16 9x9=81
5x5=25 10x10=100
Tick mk vài cái cho lên 210 nha !!!
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a) đặt \(A=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+...+\frac{1}{128}+\frac{1}{256}\)
\(\Rightarrow2\times A=1+\frac{1}{2}+\frac{1}{4}+...+\frac{1}{128}\)
\(\Rightarrow2\times A-A=1-\frac{1}{256}\)
\(A=\frac{255}{256}\)
phần b bn cx lm tương tự như z nha!
c) sửa đề:
\(\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+...+\frac{1}{13x14}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{13}-\frac{1}{14}\)
\(=1-\frac{1}{14}=\frac{13}{14}\)
Sửa:
d) \(\frac{1}{15x18}+\frac{1}{18x21}+\frac{1}{21x24}+...+\frac{1}{87x90}\)
\(=\frac{1}{3}x\left(\frac{1}{15}-\frac{1}{18}+\frac{1}{18}-\frac{1}{21}+\frac{1}{21}-\frac{1}{24}+...+\frac{1}{87}-\frac{1}{90}\right)\)
\(=\frac{1}{3}x\left(\frac{1}{15}-\frac{1}{90}\right)\)
\(=\frac{1}{3}x\frac{1}{18}\)
\(=\frac{1}{54}\)
`#3107.101107`
\(\dfrac{1}{2}\times\dfrac{2}{3}\times\dfrac{4}{5}\times\dfrac{5}{6}\times\dfrac{6}{7}\times...\times\dfrac{98}{99}\times\dfrac{99}{100}\)
\(=\left(\dfrac{1}{2}\times\dfrac{2}{3}\right)\times\dfrac{4}{5}\times\dfrac{5}{6}\times\dfrac{6}{7}\times...\times\dfrac{98}{99}\times\dfrac{99}{100}\)
\(=\dfrac{1}{3}\times\dfrac{4}{100}\)
\(=\dfrac{4}{300}\\ =\dfrac{1}{75}\)
\(\dfrac{1}{2}x\dfrac{2}{3}x\dfrac{3}{4}x\dfrac{4}{5}x\dfrac{5}{6}x\dfrac{6}{7}...x\dfrac{98}{99}x\dfrac{99}{100}\\ =\dfrac{1x2x3x4x5x6x...x98x99}{2x3x4x5x6x7x...x99x100}\\ =\dfrac{1}{100}\)