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a)=1/2 . 8/15 - 3/4.47/9
=4/15 - 47/12
=-73/20
b)=2-1/3 . -21/20
=2+7/20
=47/20
1) \(\frac{4}{5}.x=\frac{8}{35}\Rightarrow x=\frac{8}{25}:\frac{4}{5}\Rightarrow x=\frac{2}{5}\)
\(\frac{2}{3}.x+\frac{1}{4}=\frac{7}{12}\Rightarrow\frac{2}{3}.x=\frac{7}{12}-\frac{1}{4}\)
\(\Rightarrow\frac{2}{3}.x=\frac{1}{3}\)
\(\Rightarrow x=\frac{1}{3}:\frac{2}{3}\)
\(x=\frac{1}{2}\)
\(\frac{x}{10}=\frac{3}{10}\Rightarrow x=\frac{10.3}{10}\Rightarrow x=3\)
a) Ta có: \(\frac{-6}{12}< \frac{x}{12}< \frac{-4}{12}\Rightarrow-6< x< -4\Rightarrow x=-5\)
b) \(\frac{-6}{5}+\frac{13}{15}< \frac{x}{15}< \frac{-2}{5}+\frac{1}{3}\)
\(\Rightarrow\frac{-1}{3}< \frac{x}{15}< \frac{-1}{15}\)
\(\Rightarrow\frac{-5}{15}< \frac{x}{15}< \frac{-1}{15}\)
\(\Rightarrow-5< x< -1\)
\(\Rightarrow x=\left\{-4;-3;-2\right\}\)
( 2 x y + 2/15 ) x 3 = 4/5
( 2 x y + 2/15 ) = 4/5 : 3
( 2 x y + 2/15 ) = 4/15
2 x y = 4/15 - 2/15
2 x y = 2/15
y = 2/15 :2
y = 1/15
(2 x y + 2/15) x 3 = 4/5
2 x y + 2/15) = 4/5 : 3
2 x y + 2/15 = 4/15
2 x y = 4/15 - 2/15
2 x y = 2/15
y = 2/15 : 2
y = 1/15
7/9 x (2 - 1/3 x y) = 14/15
(2 - 1/3 x y) = 14/15 : 7/9
(2 - 1/3 x y) = 6/5
2 - y = 6/5 x 1/3
2 - y = 2/5
y = 2/5 + 2
y = 12/5
4/21 + 5 x y - 8/7 = 1/3
4/21 + 5 x y = 1/3 + 8/7
4/21 + 5 x y = 31/21
5 x y = 31/21 - 4/21
5 x y = 9/7
y = 9/7 : 5
y = 9/35
7/12 x y - 3/12 x y = 5
y x (7/12 - 3/12) = 5
y x 1/3 = 5
y = 5 : 1/3
y = 15
1. -x+20 = -(-15)-8+13
=> -x=15-8+13-20
=> -x=0
=> x=0
2. -(-10)+x=-13+(-9)+(-6)
=> 10+x=-13-9-6
=> x = -13-9-6-10
=> x = -38
3. 8-(-12)+10=-(-14)-x
=> 8+12+10=14-x
=> x = 14-8-12-10
=> x = -16
4. -(+12)+(-x)-(-3)=5-(-7)
=> -12-x+3=5+7
=> -x=5+7+12-3
=> -x=21
=> x=-21
5. 14-x+(-10)=-(-9)+(+15)
=> 14-x-10=9+15
=> -x=9+15-14+10
=> -x=20
=> x=-20
6. 12-(-17)+(-3)=-5+x
=> 12+17-3+5=x
=> x=31
7. x-(-19)-(+32)=14-(+16)
=> x+19-32=14-16
=> x=14-16+32-19
=> x=11
8. x-|-15|-|7|=-(-9)+|-5|
=> x-15-7=9+5
=> x=9+5+7+15
=> x=36
9. 15-x+17=13-(-21)
=> 15-x+17=13+21
=> -x=13+21-15-17
=> -x=2
=> x=-2
10. -|-5|-(-x)+4=3-(-25)
=> -5+x+4=3+25
=> x=3+25-4+5
=> x=29
a) B = \(\dfrac{4}{3}.\dfrac{5}{4}....\dfrac{21}{20}=\dfrac{1}{3}.1.....\dfrac{21}{1}=\dfrac{21}{3}=7\)
b) Em chịu, chưa học số âm :)