(3/5-4/7)nhân5/8
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Bài 1:
3/2 = 126/84; 2/3 = 56/84; 5/7 = 60/84
Bài 2 :
a)504
b)800
c)3675
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4/1x3+4/3x5
=4/1x3/1+4/3x5/1
=12+20/3
80/1=80
chúc bạn học tốt
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1/1x2 + 1/2x3+ 1/3x4+....+1/2009x2010
= 1/1-1/2 + 1/2-1/3+ 1/3-1/4+...+1/2009-1/2010
= 1/1-1/2010
= 2009/2010
\(\frac{1}{1\cdot2}+\cdot\cdot\cdot+\frac{1}{2009\cdot2010}\)
\(=1-\frac{1}{2}+\cdot\cdot\cdot+\frac{1}{2009}-\frac{1}{2010}\)
\(=1-\frac{1}{2010}\)
\(=\frac{2009}{2010}\)
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44 \(\times\) 5 + 18 \(\times\) 10 + 20 \(\times\) 5
= 44 \(\times\) 5 + 18 \(\times\) 2 \(\times\) 5 + 20 \(\times\) 5
= 44 \(\times\) 5 + 36 \(\times\) 5 + 20 \(\times\) 5
= 5 \(\times\) ( 44 + 36 + 20)
= 5 \(\times\) 100
= 500
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( 7x - 11 )3 = 25 . 52 + 200
( 7x - 11 )3 = 32 . 25 + 200
( 7x - 11 )3 = 800 + 200
( 7x - 11 )3 = 1000
=> ( 7x - 11 )3 = 103
=> 7x - 11 = 10
=> 7x = 10 + 11 = 21
=> x = 21 : 7 = 3
\(\left(7x-11\right)^3\)\(=\)\(2^5\)\(.\)\(5^2\)\(+\)\(200\)
\(\left(7x-11\right)^3\)\(=\)\(32.25+200\)
\(\left(7x-11\right)^3\)\(=\)\(800+200\)
\(\left(7x-11\right)^3\)\(=\)\(1000\)
\(\left(7x-11\right)^3\)\(=\)\(10^3\)
\(\Rightarrow\)\(7x-11=10\)
\(7x=21\)
\(x=21:7=3\)
\(\left(\frac{3}{5}-\frac{4}{7}\right)\times\frac{5}{8}\)
\(=\left(\frac{21}{35}-\frac{20}{35}\right)\times\frac{5}{8}\)
\(=\frac{1}{35}\times\frac{5}{8}\)
\(=\frac{5}{280}=\frac{1}{56}\)
(3/5-4/7) x 5/8
= ( 21/35 - 20/35 ) x 5/8
= 1/35 x 5/8
= 5/280 = 1/56