tìm y
a, 5/6 < y/8 < 5/4
b, 2/13 < 1/y < 3/4
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1: Áp dụng tính chất của DTSBN, ta được:
\(\dfrac{x}{7}=\dfrac{y}{13}=\dfrac{x-y}{7-13}=\dfrac{42}{-6}=-7\)
=>x=-48; y=-91
2: x/y=3/4
=>4x=3y
=>4x-3y=0
mà 2x+y=10
nên x=3 và y=4
3: =>7x-3y=0 và x-y=-24
=>x=18 và y=42
4: =>7x-5y=0 và x+y=24
=>x=10 và y=14
![](https://rs.olm.vn/images/avt/0.png?1311)
a) y + 3/7 x 21/9 = 5
y + 3/7 x 7/3 = 5
y + 1 = 5
y = 4
b) y x 3/5 - 1/2 = 4/5
y x 3/5 = 4/5 + 1/2
y x 3/5 = 13/10
y = 13/6
c) 9/8 - y + 2/5 = 1/4
y - 2/5 = 9 /8 - 1/4
y - 2/5 = 7/8
y = 51/40
d) y - 6/5 : 2/3 = 5/6
y - 9/5 = 5/6
y = 79/30
e) y : 7/8 + 3/4 = 7/4
y : 7/8 = 1
y = 7/8
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1:
a) \(=\dfrac{8}{15}\left(\dfrac{7}{13}+\dfrac{6}{13}\right)=\dfrac{8}{15}.1=\dfrac{8}{15}\)
b) \(=\dfrac{3.3-7-2.4}{12}=-\dfrac{6}{12}=-\dfrac{1}{2}\)
Bài 2:
\(\dfrac{x}{2,7}=-\dfrac{2}{3,6}\Rightarrow x=\dfrac{\left(-2\right).2,7}{3,6}\Rightarrow x=-\dfrac{3}{2}\)
Bài 3:
\(\dfrac{x}{2}=\dfrac{y}{5}=\dfrac{x+y}{2+5}=-\dfrac{21}{7}=-3\)
\(\Rightarrow\left\{{}\begin{matrix}x=\left(-3\right).2=-6\\y=\left(-3\right).5=-10\end{matrix}\right.\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, \(\frac{2}{5}\)+ y = 1
y = 1 - \(\frac{2}{5}\)
y = \(\frac{3}{5}\)
b, \(\frac{6}{8}\)- y = \(\frac{3}{5}\)
y = \(\frac{6}{8}\)- \(\frac{3}{5}\)
y = \(\frac{3}{20}\)
c, y : 6 = \(\frac{7}{4}\)
y = \(\frac{7}{4}\)x 6
y = \(\frac{21}{2}\)
d, y - \(\frac{1}{3}\)= 5 x \(\frac{2}{3}\)
y - \(\frac{1}{3}\)= \(\frac{10}{3}\)
y = \(\frac{10}{3}\)+ \(\frac{1}{3}\)
y = \(\frac{11}{3}\)
a,2/5 + y = 1
y = 1 - 2/5
y = 3/5
b, 6/8 - y = 3/5
y = 6/8 - 3/5
y = 3/10
c, y / 6 = 7/4
y = 7/4 * 6
y = 15/2
d, y - 1/3 = 5 * 2/3
y - 1/3 = 10/3
y = 10/3 + 1/3
y = 11/3
![](https://rs.olm.vn/images/avt/0.png?1311)
bài 1 : a,ta có 3/x-1 =4/y-2=5/z-3 => x-1/3=y-2/4=z-3/5
áp dụng .... => x-1+y-2+z-3 / 3+4+5 = x+y+z-1-2-3/3+4+5 = 12/12=1
do x-1/3 = 1 => x-1 = 3 => x= 4 ( tìm y,z tương tự
Bài 1:
a) Ta có: 3/x - 1 = 4/y - 2 = 5/z - 3 => x - 1/3 = y - 2/4 = z - 3/5 áp dụng ... =>x - 1 + y - 2 + z - 3/3 + 4 + 5 = x + y + z - 1 - 2 - 3/3 + 4 + 5 = 12/12 = 1 do x - 1/3 = 1 => x - 1 = 3 => x = 4 ( tìm y, z tương tự )
![](https://rs.olm.vn/images/avt/0.png?1311)
a) Ta có : \(\dfrac{5}{6}=\dfrac{5.4}{6\cdot4}=\dfrac{20}{24}\) \(\dfrac{y}{8}=\dfrac{y.3}{8.3}=\dfrac{y.3}{24}\)
\(\dfrac{5}{4}=\dfrac{5.6}{4.6}=\dfrac{30}{24}\)
Vậy 20 < y . 3 < 30
⇒ y . 3 = 21 ; 24 ; 27
Vậy y = 7 ; 8 ; 9
b) Ta có : \(\dfrac{2}{13}=\dfrac{2.3}{13.3}=\dfrac{6}{39}\) \(\dfrac{1}{y}=\dfrac{1.6}{y.6}=\dfrac{6}{y.6}\)
\(\dfrac{3}{4}=\dfrac{3.2}{4.2}=\dfrac{6}{8}\)
Vậy 39 > y . 6 > 8
⇒ y . 6 = 12 ; 18 ; 24 ; 30 ; 36
Vậy y = 2 ; 3 ; 4 ; 5 ; 6 ; 7 .