14/21=42/x
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7 x 2 = 14 7 x 4 = 28 7 x 6 = 42 7 x 3 = 21
2 x 7 = 14 4 x 7 = 28 6 x 7 = 42 3 x 7 = 21
14 : 7 = 2 28 : 7 = 4 42 : 7 = 6 21 : 7 = 3
14 : 2 = 7 28 : 4 = 7 42 : 6 = 7 21 : 3 = 7
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\(\dfrac{21}{17}\times\dfrac{13}{14}\times56\times\dfrac{3}{42}\)
\(=\dfrac{21}{17}\times\dfrac{13}{14}\times56\times\dfrac{1}{14}\)
\(=\dfrac{21\times13\times56}{17\times14\times14}\)
\(=\dfrac{3\times7\times13\times14\times2\times2}{17\times2\times7\times14}\)
\(=\dfrac{3\times13\times2}{17}\)
\(=\dfrac{78}{17}\)
#Sahara |
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1) 42/35 - [ 33/14 . 21/22 - ( 54/25 : 27/25 - 7/10 )]
= 42/35 - ( 9/4-13/10)
=42/35-19/20
=1/4
2) a) 5/21 . x/34 = 35/102
x/34=35/102 : 5/21
x/34=49/34
=> x=34
Vậy x=34
b) 15/x . 21/13 = 45/91
15/x=45/91 : 21/13
15/x=15/49
=> x=49
Vậy x=49
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\(\dfrac{\left(-9\right)\times14}{21\times\left(-45\right)}\)
\(=\dfrac{-126}{-945}=\dfrac{2}{15}\)
-----------------------
\(\dfrac{\left(-12\right)\times14}{\left(-42\right)\times\left(-6\right)}\)
\(=\dfrac{-168}{252}=\dfrac{-2}{3}\)
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\(\frac{6}{18}+\frac{-14}{21}=\frac{1}{3}+\frac{-2}{3}=\frac{-1}{3}\); ;
\(\frac{6}{13}+\frac{-14}{39}=\frac{18}{39}+\frac{-14}{39}=\frac{4}{39}\);
\(\frac{-3}{21}+\frac{6}{42}=\frac{-1}{7}+\frac{1}{7}=0\);
\(\frac{7}{21}+\frac{9}{-36}=\frac{1}{3}+\frac{-1}{4}=\frac{4}{12}+\frac{-3}{12}=\frac{1}{12}\)
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a) 7 x 5 = 35 7 x 6 = 42 7 x 8 = 56 7 x 4 = 28
35 : 7 = 5 42 : 7 = 6 56 : 7 = 8 28 : 7 = 4
b) 42 : 7 = 6 35 : 7 = 5 63 : 7 = 9 16 : 2 = 8
14 : 7 = 2 49 : 7 = 7 7 : 7 = 1 48 : 6 = 8
28 : 7 = 4 70 : =10 21 : 7 = 3 56 : 7 = 8
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b,21/17x13/14x56x3/42
=21/17x3/42x56x13/14
=21x3/17x42 x 56x13/14
=21x3/17x21x2 x 14x4x13/14
=3/17x2 x 4x13
=3/24 x 52=3x52/24
=3x52/3x8
=52/8=13/2
a, 6/7 x 16/15 x 7/6 x 21/32
=(6/7 x 7/6)x16/15x21/32
=16/15x21/32
=16x21/15x32
=16x3x7/3x5x16x2
=7/5x2=7/10
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a) (2800+14):14
=2814:14
=201
b) (2100-42):21
=2058:21
=98
Ủng hộ mk nka!!^_^
\(\dfrac{14}{21}=\dfrac{42}{x}\)
\(14x=42.21\)
\(14x=882\)
x = 63