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a: \(=\dfrac{5}{14}\left(\dfrac{2}{9}+\dfrac{7}{9}+1\right)=\dfrac{5}{14}\cdot2=\dfrac{5}{7}\)
b: \(=\dfrac{6}{8}\left(\dfrac{6}{7}-6\right)=\dfrac{6}{8}\cdot\dfrac{-36}{7}=\dfrac{-216}{56}=\dfrac{-27}{7}\)
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\(\dfrac{12}{7}=\dfrac{12\times12}{7\times12}=\dfrac{144}{84}\)
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`7/12=( 7xx7)/(12xx7)=49/84`
`9/14=(9xx6)/(14xx6)=54/84`
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1/1998 x ( 6/7 + 4/7 - 6/14 )
= 1/1998 x 1
= 1/1998
1/1998 x 6/7 + 1/1998 x 4/7 - 1/1998 x 6/14=1/1998x(6/7+4/7-6/14)=1/1998x(12/14+8/14-6/14)=1/1998x2=2/1998=1/999
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mk làm phần c trc nhé bn vì phần a,b thấy số cũng to nên làm dễ trc:
\(\frac{5\times6\times7}{12\times14\times15}=\frac{5\times6\times7}{12\times7\times2\times5\times3}=\frac{6}{72}=\frac{1}{6}\)
Bn gạch cho mk : hai số 7, hai số 5 nha.Vì mk ko biết gạch số nên bảo bn vậy mog bn hỉu.
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84/21 - (7/6 + 11/7)
= 84/21 - (49/42 + 66/42)
= 84/21 - 115/42
= 168/42 - 115/42
= 53/42
( 14 - x : 6 ) * 7 = 84
( 14 - x : 6 ) = 84 : 7
( 14 - x : 6 ) = 12
14 - x : 6 = 12
14 - x = 12 : 6
14 - x = 2
x =14 - 2
x = 12
Nhớ k cho mk nha !!!!!!!!!!!
( 14 - x : 6 ) x 7 = 84
( 14 - x : 6 ) = 84 : 7
( 14 - x : 6 ) = 12
14 - x : 6 = 12
14 - x = 12 : 6
14 - x = 2
x = 14 - 2
x = 12
Vậy x = 12