x*3/5+x*2/7 = 31/70
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![](https://rs.olm.vn/images/avt/0.png?1311)
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\(y\times\frac{3}{5}+y\times\frac{2}{7}=\frac{31}{70}\)
\(\Leftrightarrow y\times\left(\frac{3}{5}+\frac{2}{7}\right)=\frac{31}{70}\)
\(\Leftrightarrow y\times\frac{31}{35}=\frac{31}{70}\)
\(\Leftrightarrow y=\frac{1}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
X x 3/5+ Xx 3/7=31/70
=>X x (3/5+3/7)=31/70
=>X x 36/35=31/70
=>X=31/70:36/35
=>X=31/72
X x 3/5+ Xx 3/7=31/70
=>X x (3/5+3/7)=31/70
=>X x 36/35=31/70
=>X=31/70:36/35
=>X=31/72
![](https://rs.olm.vn/images/avt/0.png?1311)
a, (X+7)x8-14=66
=>(X+7)x8=66+14
=>(X+7)x8=80
=>X+7=80:8
=>X+7=10
=>X=10-7
=>X=3
b, 1+2+3+...+X=1711
<=>(X+1)xX:2=1711
=>(X+1)xX=1711x2
=>(X+1)xX=3422=59x58
Vì x<x+1 và (x+1)-x=1
=>x=58
c, X+3/5+Xx2/7=31/70
<=>Xx(1+2/7)+3/5=31/70
=>Xx9/7=31/70-3/5
=>Xx9/7=-11/70
=>X=-11/70:9/7
=>X=-11/90
d, 1/7+6/7xX=1/7
=>6/7xX=1/7-1/7
=>6/7xX=0
=>X=0:6/7
=>X=0
Chúc bạn học giỏi nha!!!
K cho mik với nhé cung bảo bình
![](https://rs.olm.vn/images/avt/0.png?1311)
x*3/5+x*2/7=31/70
x*(3/5+2/7) =31/70
x*31/35 =31/70
x =31/70 :31/35
x = 1/2
\(x.\frac{3}{5}+x.\frac{2}{7}=\frac{31}{70}\)
\(x\left(\frac{3}{5}+\frac{2}{7}\right)=\frac{31}{70}\)
\(x\left(\frac{21}{35}+\frac{10}{35}\right)=\frac{31}{70}\)
\(\frac{31}{35}x=\frac{31}{70}\)
\(x=\frac{31}{70}:\frac{31}{35}\)
\(x=\frac{31}{70}.\frac{35}{31}\)
\(x=\frac{35}{70}\)
\(x=\frac{1}{2}\)
vay \(x=\frac{1}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x\times\frac{3}{5}+x\times\frac{2}{7}=\frac{31}{70}\)
\(x\times\left(\frac{3}{5}+\frac{2}{7}\right)=\frac{31}{70}\)
\(x\times\frac{31}{35}=\frac{31}{70}\)
\(x=\frac{31}{70}:\frac{31}{35}\)
\(x=\frac{1}{2}\)
1/2 BAN NHA
TA LẤY X*(3/5+2/7)=31/70
X*31/35=31/70
X=31/70:31/35
X=1/2
\(\Rightarrow\)X*(3/5+2/7)=31/70
\(\Rightarrow\)X*31/35=31/70
\(\Rightarrow\)X=31/70:31/35
\(\Rightarrow\)X=1/2
\(x.\frac{3}{5}+x.\frac{2}{7}=\frac{31}{70}\)
\(x.\frac{31}{35}=\frac{31}{70}\)
\(x=\frac{1}{2}\)